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PHYSICS

FORM 4

NOTES

Name: ______________________

Class: ___________

Teacher: Mr. Neil Briffa

Theme 3 -The Nature of Waves

Mr. N. Briffa B.Ed (Hons.)

1

• Waves carry _______________ from one place to another. • There are two kinds of waves:

a) Transverse waves b) Longitudinal waves.

Transverse waves

Transverse waves are made up of _________________ and ____________________. Definition of a transverse wave: It is a wave in which the vibrations are _________________________ (900) to the direction of the wave.

Examples of transverse waves: ____________________, _________________, __________________.

Longitudinal waves

Longitudinal waves are made up of ______________________ and ________________________. Definition of a longitudinal wave: It is a wave in which the vibrations are ________________________ (1800) to the direction of the wave.

Example of longitudinal wave: ______________________. http://www.youtube.com/watch_popup?v=Rbuhdo0AZDU

Mr. N.Briffa

HOD



2

Wavelength ( λ ) S.I. unit: metre (m) The wavelength of a wave is the length of a single wave. It is denoted by the Greek letter λ (read as lambda). a) Transverse waves The wavelength ( λ ) for a transverse wave is the length of a single wave made up of a crest and a trough. However, it is also equal to the distance between two successive ______________ or two successive ___________________.

b) Longitudinal waves The wavelength ( λ ) for a longitudinal wave is the length of a single wave made up of a compression and a rarefaction. However, it is also equal to the distance between two successive ______________________ or two successive ___________________.

http://einstein.byu.edu/~masong/HTMstuff/WaveTrans.html

Amplitude and Displacement S.I. unit: metre (m) The displacement is the height of the wave, from its rest position. The maximum displacement is called __________________. So the amplitude is the height of a crest or the depth of a trough. The greater the amplitude, the greater the ________________ of the wave.

At which points is the displacement zero metres? _____________________________________ At which points do we measure the amplitude? _____________________________________

3 dimensional view

Mr. N.Briffa

HOD



3

Waves, cycles and oscillations

1 wave = 1 cycle = 1 oscillation

Frequency (f) S.I. unit: Hertz (Hz)

Definition: It is the number of waves in _________ second. If 5 waves are generated in one second, then the frequency = ___________.

If 100 waves are generated in one second, then the frequency = __________.

The frequency of a wave can only change if the frequency of the source changes. If you dip your finger in water 3 times in 1 second, your frequency (the source) is 3 Hz and the frequency of the waves is also 3 Hz as 3 waves are produced every second. If the waves move in deep or shallow water the frequency will still be 3 Hz as you would still be producing 3 waves in one second. Unless you change your frequency (source), the frequency of the waves will not change.

Periodic Time (T) S.I. unit: seconds (s)

Definition: It is the time taken to complete one wave. If it takes 3 seconds to complete one wave, then the periodic time = ___________.

If it takes 0.2 seconds to complete one wave, then the periodic time = __________.

f = 1 and T = 1 T f Example:

If 5 waves are produced in one second, find: a) the frequency, b) the periodic time.

_______________________________________________________________________________________

_______________________________________________________________________________________

Mr. N.Briffa

HOD



4 Frequency (f) =

no of waves in 1 second Periodic Time (T) = Time for one complete wave

Ex 1

Ex 2

Ex 3

Ex 4

Ex 5

Ex 6

Ex 7

Find the:

a) Periodic time _________________________________ b) Frequency __________________________________

Ex 8

Six waves hit a breakwater every minute. Find the: a) frequency ____________________________________________________________________ b) periodic time ____________________________________________________________________

Mr. N.Briffa

HOD



5

Ex 9

The pendulum takes 2 seconds to swing from A to B. If the horizontal distance from A to B is 1 m, find:

a) its amplitude of vibration _______________________________

b) its periodic time _______________________________________

c) its frequency __________________________________________

Ex 10

During an earthquake, the upper part of a skyscraper moves from side to side, a horizontal distance of 4 m in 1.2 seconds. Find:



c) its frequency __________________________________________

Ex 11

The ruler is placed at the edge of a table and is set to vibrate as shown. If the end of the ruler moves a vertical distance of 3 cm in 0.2 seconds, find:



c) its frequency __________________________________________

Wave Velocity (v or c) S.I. unit: metres per second (m/s) This is the velocity with which the wave travels.

Velocity = Frequency x Wavelength v = f λ (m/s) (Hz) (m)

Example 1:

Find the velocity of a wave having a frequency of 3 Hz and a wavelength of 0.4 m. _______________________________________________________________________________________ _______________________________________________________________________________________ Example 2:

Find the frequency of a wave which is moving at 2 m/s and which has a wavelength of 30 cm. _______________________________________________________________________________________ _______________________________________________________________________________________

Mr. N.Briffa

HOD



6

The Electromagnetic Spectrum

• Gamma rays have the ____________________ frequency, the _____________________ energy and the

__________________________ wavelength.

• Radio waves have the _____________________ frequency, the _______________________ energy and

the __________________________ wavelength.

Gamma rays, X-rays, Ultraviolet, Visible light, Infra-red, Microwaves and Radio waves are all

electromagnetic waves that make up the _____________________________________________. Except for

visible light, all the other waves are invisible to the human eye.

Common properties of Electromagnetic waves:

1. They are all __________________________ waves.

2. They do not need a medium to travel through, so they can travel in a ________________________.

3. They have a common ___________________ (3 x 108 m/s or 300,000,000 m/s).

4. Being waves they all carry __________________.

5. They obey the laws of reflection, refraction and diffraction.

6. They are uncharged. (not + or - )

Mr. N.Briffa

HOD



7

Approximate λ (m)

Source Use Additional information

Gamma

Is very penetrating and can be very dangerous if used inappropriately. Can be detected with a Geiger-Muller tube.

X-rays

Produced when electrons hit a metal target. Can penetrate flesh but not bones and so produces a shadow, making fractures visible. Parts of the body need to be covered with lead. Can be detected by photographic plates.

Ultraviolet

Over-exposure can lead to skin cancer. They are partly absorbed by the ozone layer. Can be detected by using fluorescent chemicals making objects glow in the dark.

Visible light

The only radiation which we can see. Can be further divided into seven colours.

Infra-red

Green house effect results when infra-red waves get trapped in the atmosphere causing global warming. These waves can be detected by using a thermometer with a blackened bulb.

Microwaves

Microwaves make the water particles contained in food vibrate causing heating. They cause burns if absorbed by the body.

Radio waves

Information is encoded into a radio wave, transmitted to a receiver where it is decoded.

Mr. N.Briffa

HOD



8

Ripple tank

Water waves are transverse waves. They can be studied in a __________________________. Architects and engineers use ripple tanks to study the best design for breakwaters before they start projects on a large scale. How do you produce straight waves in a ripple tank? By using a _____________________ that is forced to move up and down by an electric motor. How do you produce circular waves in a ripple tank? By using a _____________________ that is forced to move up and down by an electric motor. A _____________________ is an instrument that makes waves appear stationary. The ___________________ is equal to the distance between two successive wavefronts and is measured with a metre ruler.

Reflection of water waves

The angle of incidence (i) is equal to the angle of reflection (r). Draw the normal and the reflected wavefronts in each diagram.

Underline the correct answer:

After the waves are reflected: a) the wavelength ( increases, remains the same, decreases) b) the frequency ( increases, remains the same, decreases) c) the velocity ( increases, remains the same, decreases)

Mr. N

.Briffa HOD



9

Refraction of water waves

When water waves change the depth, they change direction because they change their _____________. Underline the correct answer: When the wavefronts pass from deep water to shallow water:

• the wavelength (increases, remains the same, decreases) • the frequency (increases, remains the same, decreases) • the velocity (increases, remains the same, decreases) • the wave changes direction and is refracted (towards, away from) the normal.

Underline the correct answer: When the wavefronts pass from shallow water to deep water:

• the wavelength (increases, remains the same, decreases) • the frequency (increases, remains the same, decreases) • the velocity (increases, remains the same, decreases) • the wave changes direction and is refracted (towards, away from) the normal.

http://www.youtube.com/watch_popup?v=r0088hYFuws

Mr. N.Briffa

HOD



10

Complete the diagrams below.

http://www.youtube.com/watch_popup?v=stdi6XJX6gU

If the wavefronts enter the shallow water along

the normal, they are not refracted. However

the wavelength and the speed still

_______________ in shallow water and

_________________ in deep water. The

frequency does not change.

Mr. N.Briffa

HOD



11

Question: A graph of the displacement against distance for a wave is shown in the diagram.

a) Using the graph, find the amplitude of the wave.

____________________________________________________________________________(1 mark)

b) Using the graph, find the wavelength of the wave.

____________________________________________________________________________ (1 mark)

c) If the frequency of the source is 100 Hz, calculate the velocity of the wave.

____________________________________________________________________________(2 marks)

d) The wave enters a medium and slows down. What change, if any, is there in the frequency?

____________________________________________________________________________(2 marks)

e) What change if any is there in the wavelength?

____________________________________________________________________________(2 marks)

f) How would the same graph be different if the wave had more energy?

____________________________________________________________________________(2 marks)

Mr. N.Briffa

HOD



12

Diffraction of water waves

When water waves pass through a gap they spread or __________________. The diffraction is greatest

when the gap width is similar to the wavelength of the wave. Spreading of waves is not desired in

harbours.

The narrow gap being similar to the wavelength of the waves causes more diffraction (spreading) of

waves and this would not be ideal for a harbour.

In each case, the velocity, frequency and wavelength _____________________________________.

http://www.ngsir.netfirms.com/englishhtm/Diffraction.htm

http://www.youtube.com/watch_popup?v=4EDr2YY9lyA

Mr. N.Briffa

HOD



13

Question:

Harbours have breakwaters to stop large waves.

a i) What is the wavelength of the water waves?

__________________________________________________________________________(2 marks)

ii) 5 waves hit the breakwater every 20 seconds. What is the frequency of the water waves?

________________________________________________________________________________

__________________________________________________________________________ (2 marks)

iii) Calculate the velocity of the waves.

__________________________________________________________________________ (2 marks)

b i) Complete the diagram above to show how the waves proceed after passing through the gap.

(2 marks)

ii) Explain why it would not be wise to make the gap too narrow.

________________________________________________________________________________

__________________________________________________________________________ (2 marks)

Mr. N.Briffa

HOD



14

Question: This question is about an experimental design about water waves.

a) A tank 5 m long is filled with water. Using the apparatus above, describe how one could find the speed of the water wave.

___________________________________________________________________________________

___________________________________________________________________________________

___________________________________________________________________________________

___________________________________________________________________________(4 marks) b) A student is told that the deeper the water, the less the wave velocity. Describe how he should investigate this statement. Method:

___________________________________________________________________________________

___________________________________________________________________________________

___________________________________________________________________________________

___________________________________________________________________________(3 marks) Table of results:

(2 marks) Graph:

___________________________________________________________________________ (1 mark) Precautions:

___________________________________________________________________________________

___________________________________________________________________________________

___________________________________________________________________________ (3 marks) From the shape of the graph, how could the student tell if the statement is correct?

___________________________________________________________________________________

___________________________________________________________________________(2 marks)

stopwatch

measuring tape

Mr. N.Briffa

HOD



15

SOUND

Sound energy travels in the form of longitudinal waves. A longitudinal wave is made up of _______________________ (C) and ____________________ (R). How does sound travel through air? By means of compressions and rarefactions of air particles.

Sound waves from a loudspeaker produce compressions and rarefactions of invisible air molecules. A

compression is a region in which the number of air molecules (particles) is high. A rarefaction is a

region in which the number of air molecules is low.

The speaker has a cone which is made to vibrate in and out by an electric current. When the cone

moves, out the air in front is compressed and when it moves in, the air is rarefied.

Sound is not electromagnetic in nature as it requires a medium to travel. Sound does not travel in a vacuum. If an explosion occurs in space, nothing will be heard as there the sound cannot travel. Experiment: To show that sound requires a medium to travel.

As air is pumped out by a vacuum pump, the ringing of the bell gets

lower and lower. When all the air is removed, the hammer can be seen

vibrating but no sound is heard. This experiment shows that sound does not travel in a __________________.

Mr. N.Briffa

HOD



16

The tuning fork

This is an instrument which after being struck vibrates at a certain frequency. If it has a frequency of 256Hz, it means that it vibrates 256 times in one second.

Characteristics of sound a) Pitch: Pitch is a term used by musicians to distinguish different notes.

The higher the pitch, the higher the _____________________.

b) Loudness: The loudness of a sound wave depends on how much ______________ it has.

The loudness and energy depend on the ____________________ of the sound wave. Another word for loudness is _________________.

Both sounds have the same pitch as the tuning forks vibrate at the same frequency.

So pitch and loudness are independent of each other.

c) Quality (timbre): The same note on

different instruments sounds differently even though they have same pitch and loudness.

A tuning fork of frequency

256 Hz produces a sound with a high pitch (diiing).


128 Hz produces a sound with a low pitch (dooong).


256 Hz struck hard produces a loud sound with large amplitude.

The tuning fork of frequency

256 Hz struck gently produces a quiet sound with a small amplitude.

Mr. N.Briffa

HOD



17

Question:

In the lab a student connects a microphone to an oscilloscope so that it can be used to detect sound waves. A loudspeaker producing a note of frequency 300 Hz is placed in line with the microphone. The trace obtained on the oscilloscope screen is shown in Figure 1.

Figure 1 Figure 2 Figure 3

a) Explain how a sound wave travels through the air, from the loudspeaker to the microphone.

_____________________________________________________________________________________

_____________________________________________________________________________ (2 marks)

b) If the velocity of sound in air is 330 m/s, what is the wavelength of the sound emitted?

_____________________________________________________________________________ (2 marks)

c) The student decreases the intensity (loudness) of the sound produced but does not change the frequency.

Draw the new trace produced on the screen in Figure 2. (2 marks)

d) The sound intensity is changed back to its initial value and this time the frequency is varied from 300 Hz

to 600 Hz. Draw the trace of the new note of frequency 600 Hz in Figure 3. (2 marks)

e) The loudspeaker and microphone are now placed inside a sealed jar, as shown below. The loudspeaker

produces a note of 300 Hz, and with the jar full of air the trace produced is as shown in Figure 1.

If all the air is pumped out of the jar, what trace is now seen on the oscilloscope? Explain.

_____________________________________________________________________________________

____________________________________________________________________________ (2 marks) (Total 10 marks)

Mr. N.Briffa

HOD



18

Question: The following are traces seen on an oscilloscope when 4 different sounds are produced.

A B C D Which of the figures represents:

Speed of sound ANY sound in air travels at around 330 m/s. It does not depend on pitch or loudness. The speed of sound is affected by the temperature and the material through which it travels. The higher the temperature, the _______________ the sound travels.

Material Speed of sound (m/s)

Air

Water

Steel

Reflection of sound

Sound waves are reflected when incident onto a surface. The reflected sound is called an ___________.

An echo is less loud than the original sound. This is because it has less energy. Example :

A man standing at a distance of 200 m from a large high wall, produces a sound and hears an echo after 1.2

seconds. Find the speed of sound in air.

_______________________________________________________________________________________

_______________________________________________________________________________________

A loud high pitch sound. A quiet high pitch sound. A loud low pitch sound. A quiet low pitch sound.

Mr. N.Briffa

HOD



19

Measuring the speed of sound

Method 1:

A sound is produced (e.g. by clapping once). When the sound reaches microphone X, _____________________________________. When the sound reaches microphone Y, _____________________________________. The distance d is measured with a metre rule and the formula Speed = Distance is used.

Time Method 2:

A person standing at a distance of about 100 m from a large high wall, claps his hands at regular intervals to coincide exactly with the echoes. The time taken for 50 claps is recorded. The distance for each echo heard is 2 x 100 m = 200 m The time for one echo is found by measuring the total time for 50 echoes and finding an average. ( ex. if the

total time is 30 seconds, average time = 30 ÷ 50 = 0.6 seconds)

Using the formula: Average speed = Distance = 200 m … will give the speed of sound in air. Time time for one echo

Mr. N.Briffa

HOD



20

Example :

An echo sounder in a trawler receives an echo from the sea bed 2 seconds after it is

sent. If the speed of sound in water is 1500 m/s, how deep is the sea?

_____________________________________________________________________

__________________

Question:

Luke and David are standing between 2 walls A and B, 480 m from the nearest wall. David beats his drum and Luke hears the first echo after 3 seconds.

a) Explain why Luke hears an echo.

__________________________________________________________________________(2 marks) b) Calculate the velocity of sound in air.

__________________________________________________________________________(2 marks)

c) If a second echo is heard 2 seconds later, what is the distance between the walls?

____________________________________________________________________________________

_______________________________________________________________________________________

_____________________________________________________________________________(3 marks) d) Luke tries to measure the speed of sound in a liquid. The equipment used is shown below. Explain briefly how the speed is measured.

___________________________________________

___________________________________________

___________________________________________

___________________________________________

___________________________________________

___________________________________(3 marks)

Ultrasound We can hear sounds with a frequency between ______ Hz and _________Hz. Sound waves with a frequency higher than 20,000 Hz (20 kHz) are called _____________________. Therefore ultrasound waves are just _______________ waves with a very high frequency. A dog’s whistle produces ultrasonic sounds. • Ships use an echo sounding system called sonar, which uses ultrasound to measure

the _________________________________________ and to detect ______________________________.

• Doctors use ultrasound to scan ________________________ in the body and monitor unborn babies.

• Bats and dolphins use ultrasound to know how far they are from objects and to hunt (echolocation).

• Detect flaws in welding.

Mr. N.Briffa

HOD



21

This is a question about the use of ultrasound by bats.

The first known work with ultrasound was carried out by Lazzaro Spallanzani, an

Italian scientist who wondered how bats can fly in complete darkness. He

blindfolded them and noticed that they still could fly well. He then plugged their ears

and found that they bumped into obstacles.

He concluded that they must emit sound waves which we cannot hear and then

listen to the echoes to determine the distance and direction of objects.

a) What is the normal range of hearing for human beings?

________________________________________________________________________ [1]

b) How does sound travel through air?

________________________________________________________________________ [1]

c) Is ultrasound made up of transverse or longitudinal waves?

________________________________________________________________________ [1]

d) A bat emits a sound with a frequency of 34 kHz.

(i) What is meant by the term frequency?

________________________________________________________________________ [1]

(ii) What is the value of the above frequency in Hertz?

________________________________________________________________________ [1]

(iii) Calculate the wavelength of the sound waves produced, if their speed in air is 340 m/s.

________________________________________________________________________ [1]

e) The bat is flying close to a wall and receives the reflected sound after 0.16 s.

(i) What is the reflected sound called?

________________________________________________________________________ [1]

(ii) Calculate the distance between the bat and the wall.

________________________________________________________________________ [1]

Mr. N.Briffa

HOD



22

LIGHT

• Objects which emit light are called _________________ objects.

• Objects which do not emit light themselves but reflect the light of luminous sources, are called

_______________________________ objects.

• We see things because rays either come directly from them if they are luminous, or rays coming from luminous sources are reflected by non luminous sources into our eyes.

Fill in the table below with the following items: fire, chair, shining mirror, moon, Jupiter, galaxy.

Luminous Non-luminous

Light rays

Light rays represent the direction in which light travels. Light rays may be _________________, _______________________, or __________________________. We use a ray box to produce rays in the lab.

a ray box

Mr. N.Briffa

HOD



23

REFLECTION OF LIGHT Light is reflected when it falls on a reflecting surface such as a mirror. Complete the diagram below marking, the normal, incident ray, reflected ray, angle of incidence (i), angle of reflection (r).

Laws of reflection

• The angle of incidence and the angle of reflection are __________________. • The normal, the incident and reflected ray all lie _________________________. This means that they

can be drawn on a flat sheet of paper. Example: The table below shows the angles of reflection for different angles of incidence obtained by a student during an experiment using a plane mirror and a ray box.

Angle of reflection (r) 10 25 30 40 50 Angle of incidence (i) 10 20 30 40 50

• Plot a graph of angle r (y-axis) against angle i (x-

axis).

• When the angle of incidence is 00, the angle of reflection is ___________.

• What should be the value of the wrongly read

angle of reflection? _____________.

Mr. N.Briffa

HOD



24

Experiment: Reflection

Apparatus: __________________________________________________________________________ Diagram:

Method:

_________________________________________________________________________________________

_________________________________________________________________________________________

_________________________________________________________________________________________

_________________________________________________________________________________________

Table:

Conclusion:

_________________________________________________________________________________________

_________________________________________________________________________________________

Not all surfaces are able to reflect very well the light rays falling on them. This is due to the surface itself. The smoother the surface, the better it reflects and the shinier it appears.

Angle of incidence (0) Angle of reflection (0)

Mr. N.Briffa

HOD



25

The image in a plane mirror is:

What is lateral inversion?

The word would be seen as if it were to be seen in a mirror. That makes it more difficult to read. On an ambulance the word ambulance is laterally inverted so that drivers could read it properly when they see an ambulance in their cars’ mirrors. The periscope

A periscope makes use of reflection. It consists of two plane mirrors facing

each other and placed at an angle of 450. Periscopes are useful when one

cannot see something because of an obstacle. The ones used in submarines

use prisms rather than mirrors.

Real and Virtual images

A ______________ image can form on a screen (e.g. cinema, slide projector, camera). A _____________ image does not form on a screen (e.g. mirror, magnifying lens)

• _________________________________________

_________________________________________

• _________________________________________

• _________________________________________

• _________________________________________

Complete the diagrams to show where the image forms.

Mr. N.Briffa

HOD



26

This question is about reflection. A shop sign is seen by a student at P but not by one at Q.

a) Draw a ray from the shop sign S which reaches P after reflection at the mirror. Include in your diagram, the incident ray, the reflected ray and the normal. (2 marks) b) Show on the diagram the position of the image of S. (1 mark) c) What can be said about: (i) the image distance and the object distance? _____________________________________________________________________________(1 mark)

(ii) the type of image?

____________________________________________________________________________ (1 mark)

d) Why does the boy find it difficult to read the sign?

____________________________________________________________________________ (1 mark)

e) Why can’t the student at Q see the image?

____________________________________________________________________________ (1 mark)

Mr. N.Briffa

HOD



27

REFRACTION OF LIGHT (bending of light) When light travels through different substances or media, it changes direction because it changes ______________________. This phenomenon of bending is called _______________________. Which of these is an optically denser medium? (glass, water, air). Which of these is an optically less dense medium? (glass, water, air).

When light passes from one medium to another, its speed changes. When light passes from an optically less dense medium (e.g. air) to an optically denser medium (e.g. glass) its speed ____________________ and it is bent or refracted __________________ the normal. When light passes from an optically dense medium (e.g. glass) to an optically less dense medium (e.g. air) its speed ___________________ and it is bent or refracted ___________________ the normal. We can compare this effect to a fast car moving on a road that gets stuck in mud and comes out again.

Mr. N.Briffa

HOD



28

Other facts about Refraction

The refractive index (η)

Every optical material has its own refractive index (e.g. η for glass =1.5, η for water = 1.33). The greater the refractive index of a material, the more is it able to:

a) ________________________________________________________________

b) ________________________________________________________________

A ray is not refracted (bent) when it is enters normally (along the normal).

An object under water appears at a different depth.

A pencil immersed in water appears bent because of refraction.

Which material has the greatest

refractive index? Why?

_______________________________

_______________________________

_______________________________

_______________________________

Mr. N.Briffa

HOD



29

Example: As light passes from air to glass its speed decreases from 3 x 108 m/s to 2 x108m/s. Find the refractive

index of glass.

______________________________________________________________________________________

______________________________________________________________________________________

• The _____________ depth is the depth at which the object is.

• The _____________ depth is the depth at which the image forms and the object appears to be.

• The apparent depth is always ___________ than the real depth.

Example: A diver is at a depth of 6m. He appears to be at a depth of 4.5m. Find the refractive index of water. ______________________________________________________________________________________

______________________________________________________________________________________

Refractive index (η) = speed of light in air speed of light in medium

Refractive index (η) = real depth apparent depth

Mr. N.Briffa

HOD



30

Total Internal REFLECTION

The incident ray is not refracted because it enters the glass

block along the _______________. When the angle of

incidence is very small, there is a strong refracted ray and a

very weak ray that is reflected back into the glass block.

As the angle of incidence is increased by moving the ray box,

at some point the angle of refraction becomes _________. At

this point the angle of incidence is called the

_______________________________.

When the critical angle is ________________ there is

________________________________________.

At some point no light from the torch emerges to the surface. Explain why? ______________________________

______________________________

______________________________

______________________________

______________________________

Mr. N.Briffa

HOD



31

Reflecting Prisms

When the ray enters the face PQ it is not

refracted as it enters along the

______________. The critical angle of glass is

420 and when the ray hits the side PR, the

__________________________ is exceeded

and so there is _____________

__________________________________.

Periscope (using prisms)

One application of total internal reflection is used in this type of

periscope which uses _____________ instead of mirrors. Draw the correct position of the lower prism of the periscope. Draw a ray showing its path from the object to the observer.

Fibre Optics

Another application of total internal reflection is fibre optics. They are used by doctors in procedures such as ________________. They are also used for telecommunications. The light ray is trapped inside the solid optical fibre because each time the ______________ angle of the material is exceeded and there is total internal reflection. They are deliberately thin so that the critical angle would be exceeded more easily.

Name three advantages of fibre optics over normal wire cables in carrying information. _____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

What are the two conditions needed for total internal reflection to occur? ____________________________________________________________________________________________________________________________________________________________________________________________________________________________

Mr. N.Briffa

HOD



32

Mr. N.Briffa

HOD



33

Dispersion

White light can be split up into a spectrum of 7 different colours. This phenomenon is called _______________________. Continue the ray diagram to show the path taken by the different colours. Mark on the screen where you think might be infra-red and ultraviolet radiation. Which colour is most refracted? ___________________ Which colour travels fastest in glass? __________________

Lenses Lenses are used in optical instruments (e.g. microscopes, telescopes). There are two types of lenses:

convex (converging) lens concave (diverging) lens

The convex lens is _______________ at the centre and it bends light _______________________.

The diverging lens is ________________ at the centre and it bends light _____________________.

The centre of the lens is called the _________________________.

The line through C at right angles to the lens is called the _________________________________.

The focal point is denoted by the letter F. It is also known as _____________________.

The focal length is the distance between the ___________________ and the

________________________________ of the lens.

Mr. N.Briffa

HOD



34

Lenses Ray Diagrams

Magnifying Lens

The image is: __________________, _____________________, __________________.

Projector

The image is: __________________, _____________________, __________________.

Camera

The image is: __________________, _____________________, __________________.

Mr. N.Briffa

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35

Magnification

The magnification m is given by the formulae:

or

The image distance is the distance between the ________________ and the lens.

The object distance is the distance between the ________________ and the lens.

Example: Continue the following diagram, marking the image formed and stating its properties. Give a use for the diagram below. Calculate also the magnification by using both formulae.

_________________________________________________________________________________________

_________________________________________________________________________________________

_________________________________________________________________________________________

_________________________________________________________________________________________

_________________________________________________________________________________________

_________________________________________________________________________________________ Refer to page 34 to complete the table below

Height of image (cm) Height of object (cm) Magnification Magnifying lens

Projector

Camera

m = height of image height of object

m = image distance (v) object distance (u)

Mr. N.Briffa

HOD



36

Experiment: Finding the focal length of a converging lens (approximate method) The lens is moved until rays coming from a distant object (e.g. a window) form a sharp image on the wall (screen). The focal length would be the distance between the ______________ and the ______________________ on the wall.

The ray diagram for the above experiment would be the following:

The image is: __________________, _____________________, __________________. This method is approximate because the rays coming from the distant object may not be perfectly parallel.

Mr. N.Briffa

HOD



37

Experiment: Finding the focal length of a convex lens (accurate method) Light from the lamp passes through the hole in the screen and is refracted by the lens onto the mirror. The mirror reflects the light back to the convex lens producing an image of the hole with crosswires on the screen. The distance between the image and the lens is equal to the focal length of the lens.

Power of a convex lens

If a convex lens is thick it will be more able to bend parallel rays of light

over a short distance. Therefore the shorter the focal length, the greater the

power of the lens. Which of the lenses shown has the greatest power A, B

or C? Why? ___________________________________________________

____________________________________________________________

_____________________________________________________________

Mr. N.Briffa

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38

Object on F:

No image forms in this case. Object on 2F

The image is: __________________, _____________________, __________________.

Example: A slide is placed 8 cm away from a convex lens of focal length 12 cm. Draw a ray diagram to scale to show how the image forms. State the characteristics of the image. Find the image distance and also the magnification.

Mr. N.Briffa

HOD



39

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40

Mr. N.Briffa

HOD

Linear Motion – Theme 1 – On the Move


1

• When a car keeps moving at the same speed, we say that the car is moving at constant or

uniform __________________.

• If the driver increases the speed of the car at a constant rate, we say that there is a constant or

uniform ______________________.

• If the driver decreases the speed of the car at a constant rate, we say that there is a constant or

uniform ______________________.

Average Speed = Total Distance Total Time

This formula can be used either: • To find the average speed of an object. • When an object is moving at constant speed. • It CANNOT be used to find the speed at a point, if the object is accelerating or decelerating.

Example : An athlete runs a 40 km race in 90 minutes. Find his speed in km/h and in m/s. ________________________________________________________________________________________________________________________________________________________________________________

Symbol Unit Initial velocity

Final velocity

Time

Acceleration/Deceleration

Distance

When an object is stationary (at rest) or moves at constant speed, its acceleration is ___________. Acceleration is a vector quantity as it has ______________________ and _________________. Acceleration is defined as the _____________ of change of velocity.

Equations of motion

1) v = u + at or a = (v-u)

t

2) s = (u+v) x t

2

3) s = ut + ½ a t2

4) v2 = u2 + 2as

Mr. N.Briffa

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2

Example 1:

A sprinter increases his speed from 2 m/s to 6 m/s in 8 seconds. Find: a) his acceleration. b) the distance travelled. ________________________________________________________________________________________ ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ ________________________________________________________________________________________ Example 2:

A car moving at a speed of 20 m/s is decelerated to rest in 4 seconds. Find: a) its deceleration b) the distance travelled. ________________________________________________________________________________________ ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ ________________________________________________________________________________________ Example 3:

A car starts from rest and is accelerated at 5 m/s2 for 8 seconds. Find: a) its final velocity. b) the distance travelled. ________________________________________________________________________________________ ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ ________________________________________________________________________________________

Example 4:

A boy starts from rest and completes a 200 m race in 20 seconds. Find his: a) final velocity. b) average speed. c) acceleration. ________________________________________________________________________________________ ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Mr. N.Briffa

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3

Example 5:

An athelete runs a 100 m race. He takes 5 seconds to cover the first 30 m. If he continues to run the rest of the race at constant speed, find: a) his final velocity after 30 m.

________________________________________________________________________________________

________________________________________________________________________________________

b) his acceleration.

________________________________________________________________________________________

________________________________________________________________________________________

c) the total time to run the race.

________________________________________________________________________________________

________________________________________________________________________________________

Thinking and Braking distance

The thinking distance is the ______________ moved by the car while the driver is ______________.

The braking distance is the ______________ moved by the car while the driver is _______________. During the thinking distance we assume the car moves at ____________________________.

TOTAL STOPPING = THINKING + BRAKING

DISTANCE DISTANCE DISTANCE What affects the thinking distance? __________________________________________________________ What affects the braking distance? ___________________________________________________________

Mr. N.Briffa

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4

Example:

A car is moving at 15 m/s. The driver sees a child standing in the middle of the road and takes 0.6 seconds to

apply the brakes. If the car stops in a further 4 seconds. Find: a) the thinking distance

________________________________________________________________________________________

b) the deceleration of the car.

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

c) the braking distance.

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

d) the total stopping distance. ________________________________________________________________________________________

Mr. N.Briffa

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5

Example:

A driver is driving his car at a speed of 10 m/s. A child crosses the road and while the driver reacts, the car moves a distance of 5 m. The car is then brought to rest 6 seconds later. Find: a) the thinking time.

________________________________________________________________________________________

b) the deceleration of the car.

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

c) the braking distance.

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

d) the total stopping distance. ________________________________________________________________________________________

Mr. N.Briffa

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6

Velocity time graphs

A motorcycle moves at the same

speed of 20 m/s for 6 seconds. The

graph shows that it is moving at

_________________________ or

____________________________.

A car is driven from ___________

and its speed is increased uniformly

by 5 m/s every second. The car is

moving with a uniform

____________________ of 5 m/s2.

The speed of a car is decreased

uniformly from ________ to

_______ in ____ seconds. The car

makes a uniform

____________________.

Mr. N.Briffa

HOD



7

Example 1: A car moves at a constant speed of 20 m/s for 10 seconds. It is decelerated to rest in a further 4 seconds. Sketch a velocity time graph and find the: a) deceleration. b) total distance travelled. ________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

Example 2: The speed of a car is increased from 4 m/s to 12 m/s in 10 seconds. Sketch a velocity time graph and find the: a) acceleration. b) total distance travelled. ________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

Example 3: A car moves at a speed of 15m/s for 10 seconds. Its speed is decreased to 5 m/s in a further 3 seconds. Sketch a velocity time graph and find the: a) deceleration. b) total distance travelled. ________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

Mr. N.Briffa

HOD



8

Mr. N.Briffa

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9

Displacement time graphs

Consider a man standing at a certain distance from a door.

Example:

As time goes by, the distance between the man and the door remains _____m. This means that the man is __________________.

The man is standing against the door. Every second the man is moving a distance of ________ AWAY FROM the door. He is moving at a constant speed of ___________.

The man is standing _______ away from the door. He starts to move at constant speed TOWARDS the door. After 6 seconds he is ____________________________.

D

ispl

acem

ent (

m)

D

ispl

acem

ent (

m)

D

ispl

acem

ent (

m)

Displacement time

graphs

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10

Example : Summary: Describe the type of motion in each case.

D

ispl

acem

ent (

m)

D

ispl

acem

ent (

m)

D

ispl

acem

ent (

m)

D

ispl

acem

ent (

m)

Dis

plac

emen

t (m

)

Using the displacement time graph shown find the velocity of the moving object. __________________________________________________

__________________________________________________

__________________________________________________

Mr. N.Briffa

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11

Mr. N.Briffa

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12

Acceleration due to gravity (g)

If the marble, the iron ball and the feather are dropped from the

same height, the marble and the iron ball fall and hit the ground

exactly at the same time. This is because on Earth all objects

fall with an acceleration (g) of 9.8m/s2. The feather falls with

less acceleration because of ________ ________________.

This is negligible in the case of the marble and the iron ball.

Experiment:

Air is extracted by means of a vacuum pump.

A _____________ is created inside the tube.

The marble and feather inside the glass tube fall in the same way.

In a vacuum, there is no _____ ________________ since no air is present.

Therefore, the feather and the marble fall with an acceleration of

9.8 m/s2. This is called ‘g’, the acceleration due to _____________ or

acceleration of __________________.

Usually when we work problems, ‘g’ is taken to be 10 m/s2.

Object dropped from 1m height

Stone of mass 0.1kg

Stone of mass 5kg

Stone of 5kg in vacuum

Feather Feather in vacuum

Small parachute

Same parachute in vacuum

Typical acceleration

For falling objects which are DROPPED : ( u = 0 m/s )

s=½ g t 2

Example 1 : A ball is dropped from a certain height and takes 5 seconds to reach the ground. From which height was it released? What have you assumed in your calculation?

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

Mr. N.Briffa

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13

Example 2 : A stone is dropped from a height of 15 m. Find the time it takes to hit the ground. What have you assumed?

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

Experiment: Measuring ‘g’ the acceleration due to gravity

• When the switch is on position 1, the ________________ attracts the iron ball.

• When the switch is moved quickly to position 2, the iron ball __________ and the

_____________ starts.

• The timer stops counting when the ____________ hits the _____________.

• The distance fallen is measured with a __________________.

• Using the equation:

s=½ g t 2

g = 2 s t 2

For example, if the distance fallen is 1 m and the time recorded is 0.45seconds:

g = 2 x 1 = 9.88 m/s2

(0.45) 2

Mr. N.Briffa

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14

Mr. N.Briffa

HOD

Newton’s Laws of Motion – Theme 1 – On the move

Mr. N. Briffa B. Ed. (Hons)

1

Inertia is the reluctance (laziness) to change _____________________________. The greater the __________ of an object, the greater its inertia.

Examples of INERTIA in everyday life:

Inertia makes it difficult to run fast the first few metres of a race. The athlete’s body is at rest and does not want to change its state of motion. It wants to remain at rest. However, once the athlete gains speed, it would be difficult to stop,

as the body does not want to change its state of motion. It wants to keep on moving.

When the sheet of paper is pulled rapidly, the coin falls into the glass. The coin is at rest and does not want to change its state of motion.

It is hard to push a stationary object. The van is at rest

and wants to remain at rest. It does not want to change its state of motion.

When a car stops suddenly, the body moves forward due to inertia. Seatbelts prevent the forward motion caused by inertia. Airbags also help to prevent injury. Inertia can kill. Website about crashtests: http://regentsprep.org/regents/physics/phys01/accident

Newton’s 1st law: (The law of INERTIA)

An object stays at ________ or continues to move at

___________ speed unless an external force acts on it.

When a fan is switched on, it rotates very slowly in the first few seconds. It is reluctant to start moving. When it switched off, it continues to rotate for some time as it is again reluctant to change the state of motion.

Isaac Newton

1643-1727

Mr. N.Briffa

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2

The Resultant Force (Unbalanced Force)

Example 1:

_______________________________ In this case the object would __________________ to the _____________. Example 2: Name the forces:

F1 __________________________________

F2 __________________________________ Force F1 is equal to 16 000 N and force F2 is equal to 4000 N. Find the resultant force acting on the car. ________________________________________________________________________________________

________________________________________________________________________________________

In this case the car would __________________ to the _____________. Example 3:

The resultant force in this case is 0 N. In this case the object can be either: a) _________________________________

or b) __________________________________

Mr. N.Briffa

HOD



3Find the resultant force and state the type of motion in each case.

Resultant Force = ________________________________ Type of motion = ________________________________





Suggest a value for the air drag if the car is: a) moving at constant speed. ______________________________________ b) accelerating. ______________________________________

Mr. N.Briffa

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4

Example 1: Find the resultant force acting on an object having a mass of 6 kg and which is being accelerated at 5 m/s2. ___________________________________________________________________________________

Example 2: If the object has a mass of 3 kg, find: a) resultant force __________________________ b) acceleration _____________________________________________________________________

Example 4: A rope is used to lift an object of mass 30 kg.

a) Name the force caused by the mass of the object and label it in the diagram.

____________________________________________________________________

b) What is the value of the tension when the object is stationary?

____________________________________________________________________

c) What is the value of the tension when the object is lowered at constant speed?

____________________________________________________________________

d) What is the value of the tension when the object is lifted at constant speed?

____________________________________________________________________

e) Suggest a value for the tension when the object is accelerated upward.

_____________________________________________________________________

Newton’s 2nd law: ( F = m a )

The resultant force is the product of ________ and _________________.

F = m a (N) (kg) (m/s2)

Mr. N.Briffa

HOD



5Example 3: A van is travelling on a horizontal road at constant velocity. The forces acting on the van are shown in the diagram below. The force F produced by the engine is 500 N.

a) Name the force P and calculate a value for it. _____________________________________________

b) Name the force Q and calculate a value for it. _____________________________________________

c) Calculate the mass of the van. __________________________________________________________ The engine force F is suddenly increased to 1200 N. Calculate: d i) the resultant force driving the van forward assuming there is no change in Q. _____________________________________________________________________________________ ii) the acceleration of the van. _____________________________________________________________________________________

Definition: Momentum is the product of _____________ and ___________________. S.I. units: kg m/s Other units: kg cm/s Momentum is a ________________ quantity as it has magnitude and direction. Example: Find the momentum of a car of mass 2000 kg moving at 25 m/s.

________________________________________________________ Which one has more momentum in each case? (Use the signs >, < or =) Car moving at 20 m/s. Same car moving at 35 m/s.

Car moving at 20 m/s. Truck moving at 20 m/s.

Car moving at 20 m/s. Aeroplane at rest on the runway.

Car of mass 1000 kg moving at 20 m/s. Truck of mass 5000 kg moving at 4 m/s.

Momentum = mass x velocity (kg m/s) (kg) (m/s)

Mr. N.Briffa

HOD



6Example 4: When accidents happen at sea, injured persons are often rescued by helicopter as shown in the diagram.

a) If the mass of the helicopter is 1500 kg, what upward force

must be produced by the rotation of the rotor blades to keep

the helicopter at constant height? Explain.

________________________________________________

________________________________________________

________________________________________________

b) The injured person and the rescuer have a combined mass of 120 kg. They have belts attached to their waists. A rope, which is hooked to these belts, is then wound up by an electric motor in the helicopter. After a brief acceleration, the two people rise vertically at a constant speed of 10 m each minute.

i) What is the tension in the rope as it is drawn into the helicopter at constant speed? _____________________________________________________________________________________

ii) Is the tension in the rope during the acceleration likely to be greater than, less than or equal to your answer in part b i)? Explain.

_____________________________________________________________________________________

_____________________________________________________________________________________

iii) The acceleration while they are being lifted is 0.5 m/s2. Calculate the value of this tension.

_____________________________________________________________________________________

_____________________________________________________________________________________

c) Calculate the power of the motor when the people at the end of the rope are rising at a constant speed.

(Assume the process is 100% efficient).

_____________________________________________________________________________________

_____________________________________________________________________________________

Mr. N.Briffa

HOD



7Example 5: A car starts from rest and reaches a speed of 20 m/s in 5 seconds. If it has a mass of 1500 kg, Find: a) the acceleration. _____________________________________________________________________

b) the resultant force. ___________________________________________________________________

c) initial momentum. ___________________________________________________________________

d) final momentum. ____________________________________________________________________

e) change in momentum. ________________________________________________________________

Example 6: A driver of mass 80 kg loses control of his car which is moving at 10 m/s, and crashes into a wall. He comes

to rest in 0.5 seconds. Find:

a) the deceleration of the driver ___________________________________________________________

b) the average decelerating force of the seatbelt on the driver if it is to hold him firmly in his seat.

_____________________________________________________________________________________

Example 7: High flying birds such as mallard ducks could be

a source of danger to aircrafts because if they

collide with the windscreen, the resulting impact could cause

serious damage to the aircraft. Fifteen mallard ducks each of mass

1kg, travelling at 20 m/s collide with an aeroplane. The aeroplane

of mass 2000 kg is travelling with a velocity of 200 m/s in the

opposite direction.

a) Calculate the momentum of the aeroplane before the collision. ________________________________

b) Calculate the momentum of the ducks before the collision. ___________________________________

c) Calculate the total momentum of the plane and mallard ducks before collision. ___________________

____________________________________________________________________________________

An object moving to the right has a ________________ momentum. An object moving to the left has a _________________ momentum.

Mr. N.Briffa

HOD



8d) One of the mallard ducks hits the aeroplane windscreen. Calculate the impact force on the windscreen, if

the collision lasts for 0.001seconds. ___________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

e) The aeroplane windscreen is designed to withstand an impact force of 5.0 x 104 N. Will it break or not?

________________________________________________________________________________________

Newton’s 2nd law : (Everyday examples)

F = m a and a = (v – u) and so F = m (v – u)

t t

or F = mv - mu = (change in momentum) t time

Prolong time of

impact to decrease

force.

Shorten time of

impact to increase

force.

Airbags deform on impact to prevent

injury.

Seat belts need to stretch slightly so that the passengers are not

hurt.

Crumple zones are positions in the car

body which deform on impact to prevent injury

to passengers.

A nail penetrates the wood easier if it is given a sharp blow.

It is easier to catch a ball if your hand is

moved slightly backwards.

Mark with a the correct option in each case.

Mr. N.Briffa

HOD



9 Prolong time of

impact to decrease

force.

Shorten time of

impact to increase

force.

You kick the ball harder if you give it a sharp

kick.

Flexing knees after jumping prevents

injury.

Packaging material is soft to prevent objects

from breaking.

The inside of a crash helmet is padded with soft material to protect the person from head

injuries.

The golf ball travels faster if it is given a

sharp strike.

Car shock absorbers are very useful if you are driving along a bumpy

road.

Mr. N.Briffa

HOD



10Example 8:

a) A car advert specifies that the car can reach a speed of 25 m/s from rest in 18 seconds. Calculate the acceleration of the car.

________________________________________________________________________________________

________________________________________________________________________________________

b) Cars are tested for safety during accidents in special laboratories.

i) When a car crashes into a wall, the person continues to move forward. Explain why this happens.

____________________________________________________________

____________________________________________________________

ii) Seatbelts are very useful to prevent injury. What is the main use of a seatbelt?

________________________________________________________________________________________

________________________________________________________________________________________

iii) Seatbelts are slightly elastic and stretch slightly before stopping the passenger from moving

forward. What is the advantage of this? ________________________________________________________________________________________

________________________________________________________________________________________

iii) Airbags are designed to open in front of passengers in the case of an accident. Suggest a way in

which an airbag can decrease the force of impact.

________________________________________________________________________________________

________________________________________________________________________________________

Mr. N.Briffa

HOD



11

The air track

Finding the average speed of a glider on an airtrack

The formula SPEED = DISTANCE is used. TIME When the front of the glider reaches the light gate, the timer ___________. When the back part of the glider passes the light gate, the timer ____________. The distance is equal to the length of the glider and is measured with a metre ruler. Example: A glider has a length of 10 cm. It takes 0.4 seconds to pass through the light gate. Find the average speed of the glider. ________________________________________________________________________________________

Mr. N.Briffa

HOD



12 On a LEVELLED airtrack the glider will move at CONSTANT SPEED when slightly pushed

When the glider is slightly pushed the time recorded on each timer is the _________. This means that the

glider is neither _________________ nor ___________________. It is moving at __________

______________. The speed in each case can be found by using Speed = Distance/Time. The air track is

levelled by using a ________ _______________. ________________________________________________________________________________________ According to Newton’s second law:

F = m a and so a = F m a ∝ F acceleration and Force are ____________ proportional.

( the greater the force the ___________ the acceleration). e.g. The harder you push a shopping trolley the more it will accelerate.

a ∝ 1 acceleration and mass are ____________ proportional. m ( the greater the mass the ____________ the acceleration).

e.g. The greater the mass of the shopping trolleys the less they will accelerate.

Mr. N.Briffa

HOD



13Experiment:

The GREATER the Force the GREATER the acceleration ( a ∝∝∝∝ F )

A weight (force) is used to pull the glider. The glider is released and its acceleration is noted on the data logger. This is repeated several times by adding more ___________________ to increase the force. It is noted that as the force to pull the glider is increased the ______________________ increases. So acceleration and force are ____________________ proportional. Table of results:

Force (N) Acceleration (m/s2)

Sketch the graph that would be obtained:

Mr. N.Briffa

HOD



14Experiment:

The GREATER the Mass the SMALLER the acceleration ( a ∝∝∝∝ 1/m )

A weight (force) is used to pull the glider. The glider is released and its acceleration is noted on the data logger. This is repeated several times by adding more ___________________ on top of each other to increase their ____________. It is noted that as the mass of the gliders is increased, the acceleration ____________________. So acceleration and mass of gliders are ____________________ proportional. Table of results:

Mass of Gliders (kg) Acceleration (m/s2)

Sketch the graph that would be obtained:

Mr. N.Briffa

HOD



15

Terminal Velocity

The feather is dropped from a certain height. Initially its speed increases and so there is an ______________________. At this point the _____________ of the feather is greater than the _________ _________________. However the air resistance increases until it is equal to the ______________ of the feather. At this point the resultant force is equal to ___ N. The feather does not accelerate any longer and reaches it maximum constant velocity also known as ____________ ______________.

Determine whether each of the following will reach terminal velocity. A table tennis ball falling a height of 30 m. Yes

A raindrop.

An iron ball falling a distance of 5 m.

A parachutist falling down.

A feather falling a height of 20 cm.

An iron ball falling a distance of 5 m in oil. Simulation terminal velocity: http://www.physicsclassroom.com/mmedia/newtlaws/sd.html

Newton’s 3rd law:

For every ___________ there is an equal and opposite _________________.

Mr. N.Briffa

HOD

Momentum and Collisions - Theme 1 – On the Move


1

Momentum is the product of _____________ and ____________________. The SI unit is _____________.

Types of collision:

1. A collision in which the objects STICK TOGETHER after colliding.

2. A collision in which the objects SEPARATE after colliding.

3. An __________________ occurs when two combined objects separate by moving in opposite directions. State whether in each case, the objects will stick together, separate or move in opposite direction (explosion) Objects

stick together Objects separate

Explosion

Toy car A hits toy car B and they move on together.

Toy car A hit toy car B which is at rest. A stops and B moves off.

Toy car A and B are held together by a spring. They are released and then they move in opposite directions.

Firing a gun.

Stepping off a skateboard.

Rubber ball hitting the floor.

Plasticine hitting the floor.

A white billiards ball hitting a red one.

Hot gases coming out of a rocket.

Cork shooting high after opening champagne.

Kicking a ball.

An ice skater skating towards another one, moving on together after

colliding.

A bumping car hitting a wall.

Jumping into mud.

Inflating a balloon without tying a knot and letting it go of.

The Law of conservation of Momentum:

The total momentum ______________ collision is equal to the total momentum _______________, provided that there are ____________________________________. (e.g. friction).

Mr. N.Briffa

HOD



2

Example: (Objects stick together after collision) A trolley A of mass 2 kg moving at 3 m/s collides with a stationary trolley B of mass 3 kg. If the trolleys move on together after impact, find their common velocity.

Total Momentum Before impact = Total Momentum After impact m1v1 + m2v2 = (m1+m2) v3

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________ The same question can be asked as follows:

a) Find the momentum of trolley A before collision. ______________________________________________ b) Find the momemtum of trolley B before collision. ______________________________________________ c) What is the total momentum before collision? _________________________________________________ d) What is the total momentum after collision? __________________________________________________ e) Find the common velocity after the collision. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ f) Find the total K.E. before the collision. ______________________________________________________ g) Find the total K.E. after the collision. _______________________________________________________ h) Find the K.E. ‘lost’ during the collision. _____________________________________________________ i) Is K.E. conserved in this case? Why? _______________________________________________________

So only _________________ is conserved.

_________ is not conserved when objects stick together.

Mr. N.Briffa

HOD



3

This question is about momentum and collisions. a) Define the momentum of an object and state its units. ______________________________________________________________________________________(3) b) The diagram shows an experiment on collisions between trolleys. Both trolleys have a mass of 2 kg. Trolley A moving at 1.5 m/s collides and sticks to trolley B which is at rest.

i) What is the momentum of A before collision?

_____________________________________________________________________________________ (1)

ii) What is the momentum of B before collision?

_____________________________________________________________________________________ (1)

iii) What is the total momentum before the collision?

_____________________________________________________________________________________ (1)

iv) What is the total momentum after? Explain.

_____________________________________________________________________________________ (3)

v) What is the velocity of the trolleys after the collision?

_____________________________________________________________________________________

_____________________________________________________________________________________

_____________________________________________________________________________________ (2)

vi) What is the kinetic energy of A before the collision?

_____________________________________________________________________________________

_____________________________________________________________________________________ (3)

vii) What is the total kinetic energy of A and B after the collision?

_____________________________________________________________________________________

_____________________________________________________________________________________ (2)

viii) Can you explain the difference between the answers in vi) and vii)?

_____________________________________________________________________________________ (4)

Mr. N.Briffa

HOD



4

Example: (Objects separate after collision) A trolley A of mass 4 kg moving at 9 m/s collides with a stationary trolley B of mass 2 kg. If after colliding, trolley A moves at a speed of 3 m/s, find the speed at which trolley B moves off.

Total Momentum Before impact = Total Momentum After impact m1v1 + m2v2 = m1 v3 + m2v4

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Example: A sphere X of mass 4 kg moving a 1 m/s collides with an identical sphere Y which is at rest. If X stops: a) Find the speed of sphere Y after collision. b) Is K.E. conserved in this case?

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

So ______________ but also ____ can be conserved when objects separate.

Mr. N.Briffa

HOD



5

Example: A minibus of mass 2000 kg travelling at 10 m/s collides head-on with a car of mass 1200 kg and which is moving at 30 m/s in the opposite direction. If the two vehicles stick together on impact, find their common velocity and state in which direction they move.

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Explosions When an explosion occurs the two objects separate and have an equal and opposite momentum. Explosions are related to Newton’s 3rd law which states that for every _______________ there is an equal and opposite ________________.

The total momentum before and after an explosion is 0 kgm/s because momentum is ________________.

Total Momentum before explosion = Total momentum after explosion 0 = m1v1 + m2v2

Mr. N.Briffa

HOD



6

Example 1:

The velocity of a bullet of mass 5 g after being fired is 60 m/s. If the mass of the gun is 4 kg, find the recoil velocity of the gun.

Total Momentum before explosion = Total momentum after explosion 0 = m1v1 + m2v2

________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ ______________________________________________________________________

The same question can be asked as follows:

a) What is the total momentum before the gun is fired? Why?

________________________________________________________________________________________

b) What is the total momentum after the gun is fired? Why?

________________________________________________________________________________________

c) Find the momentum of the bullet after it is fired.

________________________________________________________________________________________

d)What is the momentum of the gun after it fires the bullet? Explain.

________________________________________________________________________________________

e)Find the recoil velocity of the gun.

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________

________________________________________________________________________________________ Example 2:

A man of mass 70 kg jumps out of a boat with a speed of 3 m/s. The boat of mass 300 kg moves backwards. a)Why does the boat move backwards? ________________________________________________________________________________________ b)Find the speed at which the boat moves backwards. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Mr. N.Briffa

HOD



7

Example 3:

The diagram shows two stationary trolleys separated by a compressed spring and held together by a thread. The mass of trolley A is 2 kg and that of B is 1 kg. When the thread is cut, the trolleys move rapidly apart. a) Which force is causing the movement of the trolleys? ________________________________________________________________________________________ b) What is the total momentum before and just after the thread is cut? Why? ________________________________________________________________________________________________________________________________________________________________________________ c)If trolley A moves off with a speed of 0.25 m/s, calculate the speed at which trolley B moves off. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Example 4: The diagram shows two girls on roller skates. Nicole has a mass of 25 kg while Roberta has a mass of 20 kg. They are initially at rest. a) What is the total momentum before they push each other? Why?

________________________________________________________________

b) Is momentum a scalar or vector quantity? Why?

________________________________________________________________

c) Soon after they push each other, Nicole moves at a speed of 2 m/s. Calculate her momentum.

________________________________________________________________________________________

d) What is the momentum of Roberta at this point? Why? _______________________________________________________________________________________

_______________________________________________________________________________________

e) Find the speed at which Roberta starts to move. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ ______________________________________________________________________

______________________________________________________________________

________________________________________________________________________________________

Mr. N.Briffa

HOD



8

Experiment:

To prove the LAW OF CONSERVATION OF MOMENTUM ( objects sticking together)

Method: Some plasticine is attached to glider 1 which is then slightly pushed. It passes in front of the first photodiode.

It then hits glider 2 which is at ___________. The two gliders ______________________________ and pass

in front of the second photodiode.

Results: The mass of the first glider (m1) and the second glider (m2) is found by using a ________________________.

v1 is the velocity of the _____________ glider BEFORE collision. It is read on data logger ____.

v2 is 0 m/s because glider 2 is at __________ BEFORE collision.

v3 is the velocity of ____________ gliders AFTER collision. It is read on data logger ____.

Calculation: Total momentum before = m1v1 + m2v2

Total momentum after = (m1+m2) v3 Precautions: • The air track is leveled with a ___________________________.

• A constant flow of air is checked to be present so that there is no __________________ between the

gliders and the airtrack.

Conclusion: The total momentum before collision is found to be equal to the total momentum after and so momentum is _________________________ in an inelastic collision.

Mr. N.Briffa

HOD

Electricity – Theme 5 – Part 1 -Electricity in the Home


1

THE STRUCTURE OF THE ATOM

• All matter is made up of very small particles called ___________.

• The centre of the atom is called the _____________.

• The nucleus contains ___________ and _________. Moving on the

outer surface, there are very small particles called _____________.

• A proton has a ______________ charge.

• An electron has a _____________ charge.

• A neutron is neutral and has _______________. In an atom the NUMBER OF ELECTRONS = NUMBER OF PROTONS. Therefore the atom is overall uncharged. It is ___________________. However, an atom may become charged when it loses or gains electrons.

When rubbed with a cloth, POLYTHENE becomes _____________________ charged.

When rubbed with a cloth, PERSPEX (or cellulose acetate) becomes ___________________ charged.

This atom has a lack of electrons. It lost ___ electrons. So it is ______________ charged. This atom has an excess of electrons. It gained ___ electron. So it is ______________ charged.

Only the electrons can move .

The protons and neutrons are

‘imprisoned’ in the _____________.

Law of charges

LIKE charges (- - or ++) ___________,

UNLIKE charges (+ -) ____________.

Mr. N.Briffa

HOD



2

Charging by FRICTION If a polythene strip is rubbed against a cloth, electrons would move

from the _____________ to the _________________. The

polythene becomes _____________ charged because it ends up with

an ______________ of electrons. The cloth becomes

___________________ charged because it ends up with a

_____________ of electrons.

If a perspex strip is rubbed against a cloth electrons would move

from the _____________ to the _______________. The perspex

becomes _____________ charged because it ends up with a

____________ of electrons. The cloth becomes

___________________ charged because it ends up with an

_____________ of electrons.

Charged objects lose their charge faster in wet and humid conditions.

Result

Positive Positive

Negative Negative

Positive Negative

Positive Neutral

Negative Neutral

Neutral Neutral

Mr. N.Briffa

HOD



3CONDUCTORS AND INSULATORS

Some materials allow current to flow through them. They are called _______________. Conductors have

loosely bound electrons called __________ electrons. The greater the number of free electrons, the better

the conductor. Good conductors of electricity include gold, silver, copper and aluminium.

Some materials do not allow current to flow through them. They are called ________________. Instead of

free electrons, they have strongly bound electrons. Insulators do not conduct electricity. Wood, plastic,

rubber, cork and polystyrene are insulators.

Conductor/Insulator Bulb lights (yes/no)

Wooden bar

Plastic ruler

Metal ruler

Earthing: If a charged metal object is earthed with a conductor it becomes ________________.

_______________________________

_______________________________

_______________________________

_______________________________

_______________________________

_______________________________

_______________________________

_______________________________

_______________________________

_______________________________

Mr. N.Briffa

HOD



4

Mr. N.Briffa

HOD



5

Andre Ampere 1775 -1836

Charge and Current

• The amount of electrons present on the sphere is called ________________. • The electrons flowing down to earth are called _________________.

Symbol Unit Example Charge Current

Q = I t Charge = Current x time

Example : Find the amount of charge present in a circuit if an electric current of 5 A flows every 2 minutes. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Electrical components

Picture Symbol Use

Cell

Battery

Power supply (d.c)

When a negatively charged sphere is earthed as

shown, __________ flow from the sphere to earth.

The ________________ gives a reading while the

electrons are flowing down. This simple experiment

shows that current is a flow of ____________. The

flow of current lasts for a very short time until the

sphere becomes _____________. The greater the

charge on the sphere, the greater the

______________ that will flow.

Mr. N.Briffa

HOD



6

Bulb/Lamp

Open switch

Closed switch

Ammeter

Voltmeter

Multimeter

Resistor

Variable resistor (rheostat)

Conventional current and Electron flow

Before electrons were discovered, scientists believed that current flowed from the positive to the negative terminal of a cell. Later, they realized it was a mistake. It was too late to redefine all the electrical Physics, so the inconvenience holds to this day. In the coursework we will use __________________________.

Conventional current is the way current flows from the ____________ to the __________ terminal of the cell.

Electron flow is the way electrons flows from the _____________ to the _______________ terminal of the cell.

Mr. N.Briffa

HOD



7

Alessandro Volta 1745 -1827

Voltage

The difference in the number of electrons between the terminals of a cell is called ____________. The greater the difference, the greater the voltage. For ___________ to flow, voltage needs to be present. If there is no voltage there can be no current flowing. E.m.f stands for ________________________________ and is the voltage across a cell. P.d stands for ___________________________ and is the voltage across the circuit. Both e.m.f. and p.d . are measured in _____________.

E = Q V Work/Energy = Charge x Voltage

Example: Find the electrical energy used if the charge is 5 C and the potential difference is 12 V. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

These 3 lamps are connected in _________. If one ___________, the others would ________________.

These 2 lamps are connected in ____________. If one ___________, the others would ___________________. Mr. N

.Briffa HOD



8

Georg Ohm 1789 -1854

Resistance The opposition to current flow is called __________________. Resistance depends on: a) ____________________ (the resistance due to the nature of the material itself).

b) __________________ ( the thicker the wire, the _______________ the resistance).

c) ___________________ ( the longer the wire, the ____________ the resistance).

d) ___________________ ( the higher the temperature, the ________________ the resistance).

The best conductors (e.g. gold) have the _________________ resistance. Insulators have an infinitely ______________ resistance.

Measuring instruments

Current is measured by using an _______________. It is always connected in ____________ and has a _______________ resistance so that the measured current (i.e. with the ammeter in the circuit) is as close as possible to the current in the component when the ammeter is not connected in the circuit.

Voltage is measured by using a ___________________. It is always connected in _________________ and has a _____________ resistance so that the measured p.d. (i.e. with the voltmeter in the circuit) is as close as possible to the p.d. across the component when the voltmeter is not connected in the circuit.

Label the measuring instruments in each diagram.

The brightness can be controlled by using the _____________________ (rheostat).

High resistance - _______ current - Lamp is ________.

Low resistance - _______ current - Lamp is __________.

Mr. N.Briffa

HOD



9

V = I R Voltage = Current x Resistance

(Volts) (Amps) (Ohms)

Example: A current of 0.5 A passes through a resistor of resistance 10 Ω. Find the voltage across it. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

EQUATIONS:

1. Q = It

2. E = Q V

3. V = I R

4. E = V I t

5. E = V2 t

R

6. E = I2 Rt

Finding the RESISTANCE of a metal wire To find the resistance of a metal wire we need to know its voltage and its current (R= V/I).

Example: The p.d. across a resistor is 2 V and a current of 4 A flows through it. Find:

a) the resistance of the resistor. ____________________________________________________________________________________________________________________ b) the energy dissipated by the resistor as heat in 3 minutes. ____________________________________________________________________________________________________________________ _____________________________________________________________

The voltage is noted on the ______________. The current is noted on the ______________. The equation R = V/ I is used. The resistance of any component can be found in this way. (e.g filament lamp, resistor etc.)

Mr. N.Briffa

HOD



10OHM’S LAW

OHMIC and NON-OHMIC conductors

• __________________ conductors obey Ohm’s law and the graph will be a straight line. Voltage and current will be ______________ proportional. (eg. metals, constantan wire)

• __________________ conductors do not obey

Ohm’s law and the graph will not be a straight line. Voltage and current will not be directly proportional (eg. filament lamp, themistor, diode).

_____________ is directly proportional to ____________

as long as the _______________ remains constant.

Experiment: The voltage is noted on the ________________. The current is noted on the ________________. This is repeated several times by changing the current with the ___________________________. Table:

Voltage (V) Current (A)

Precaution: _______________________________ __________________________________________________________________________________ Graph:

The gradient of the graph (∆Y/∆X) gives the ____________.

Metal

Filament lamp

Thermistor

Mr. N.Briffa

HOD



11Example 1:

Example 2:

Example 3:

Complete the diagrams to show how voltage may divide in series and parallel circuits

a) Find the total resistance _____________________________ b) Find the total current flowing _________________________ c) Find the voltage across the 6Ω resistor. ______________________________________________________________________________________________________ d) Find the voltage across the 2Ω resistor. ___________________________________________________ ___________________________________________________

a) Find the total resistance _____________________________ b) Find the total current flowing _________________________ c) Find the voltage across the 5 Ω resistor. ______________________________________________________________________________________________________ d) Find the voltage across the 1Ω resistor. ___________________________________________________ ___________________________________________________

a) Find the voltage across the 4 Ω resistor. _________________ ___________________________________________________ b) Find the voltage across R ____________________________ c) Find the resistance of R.______________________________ ______________________________________________________________________________________________________ ___________________________________________________

Mr. N.Briffa

HOD



12 Example 4:

Example5:

Example 6:

a)Find the voltage across the 12Ω resistor . ___________________________________________________ b)Find the voltage across the 6Ω resistor . ___________________________________________________ c) Find the current in the 12Ω resistor. ______________________________________________________________________________________________________ d) Find the current in the 6Ω resistor. ___________________________________________________ e) Which resistor has more current flowing through it? Why? ______________________________________________________________________________________________________

a) Find the voltage across AB. ___________________________________________________ b) Find the voltage across BC. ___________________________________________________ c) Find the current in the 8Ω resistor. ______________________________________________________________________________________________________ d) Find the current in the 2Ω resistor. ___________________________________________________

a) Find the voltage across AB . __________________________________________ b) What is the voltage across BC? __________________________________________ c) What is the voltage across CD? __________________________________________ d) Find the current in the: i ) 2 Ω resistor ______________________________ ii ) 3 Ω resistor _____________________________ iii) 6 Ω resistor _____________________________

Mr. N.Briffa

HOD



13Example 7:

Example 8:

Combined resistance of resistors in parallel

The combined resistance of resistors in parallel is always less than the resistance of the smallest resistor.

a) Find the voltage across AB . ___________________________________________________ b)What is the voltage across BC ? ___________________________________________________ c) Find the current in the 3Ω resistor. ______________________________________________________________________________________________________ d) Find the resistance of R. ______________________________________________________________________________________________________ A current of 1A flows through the 2Ω resistor. a) Find the voltage across the 2 Ω resistor? ___________________________________________________ b)Find the current in the 4 Ω resistor. ___________________________________________________ c) Find the current passing through R. ______________________________________________________________________________________________________ d) Find the resistance of R. ______________________________________________________________________________________________________

The total resistance for these resistors in series is ______ Ω For two resistors in parallel the total resistance is found by using the formula: 1 = 1 + 1 so 1 = 1 + 1 = 2 + 3 = 5 R R1 R2 R 6 4 12 12 1 = 5 so R = 12 = 2.4 Ω

R 12 5



14Example 9:

a) Find the total resistance of the circuit.

________________________________________________________________________________________

________________________________________________________________________________________

b) What is the reading on the ammeter?

________________________________________________________________________________________

Example 10:

a) Find the total resistance between B and C.

________________________________________________________________________________________

b) Find the total resistance between A and C.

________________________________________________________________________________________

c) Find the current passing through the 3.5 Ω resistor.

________________________________________________________________________________________

d) Find the voltage across AB.

________________________________________________________________________________________ e) What is the voltage across BC? ________________________________________________________________________________________ f) Find the current passing through the 2 Ω resistor. ________________________________________________________________________________________ g) Find the current passing through the 6 Ω resistor. ________________________________________________________________________________________



15Semiconductor components

These devices are made up of special material (e.g silicon and germanium) that give them special properties.

Electrical component

Symbol Function

Diode

Allows current to flow in one __________________.

L.E.D

A diode that can emit _______________________.

L.D.R

A resistor whose resistance depends on _________________.

Thermistor

A resistor whose resistance depends on ___________________.

The diode:

A

B

Example: Which filament lamp will light? Why? ____________________________________________________________________________________________________________________________________________________________________________________

The lamp will light in circuit _________. In circuit A, the diode is said to be _______________ ______________. The current can flow through the circuit. In circuit A, the diode is said to be _______________ ______________. The current flowing is negligible (almost no current flows).



16

Rectification: (changing a.c to d.c)

Direct current (d.c.) A current which ___________________ __________________________________. Supplies:

Alternating current (a.c.) A current which ___________________ __________________________________. Supplies:

If a diode is connected as shown, it will allow current to flow in one direction only. Therefore it will change _______________ current to ______________ current. This process is known as _____________________________.



17 The uses of diodes: a) Rectification (changing a.c to d.c) b) Protecting equipment.

The Light Emitting Diode (L.E.D): A L.E.D is a special diode that emits ____________ when it is forward biased. The uses of a L.E.D:

a) ________________________________________________ b) ________________________________________________

Example: A L.E.D has a voltage drop across it of 2 V and needs a current of only 10 mA. If it is connected to a 9 V supply , find the resistance of a protective resistor which is needed.

__________________________________________________________________________________________________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________

If the cell is connected as shown in the diagram the radio will work because the diode will be ___________ ______________. If the cell is connected the other way round the radio would not work as the diode would now be __________ ______________. No damage would be done to the components inside the radio.

The seven segment display used in alarm clocks makes use of 7 light

emitting diodes.



18

A fixed resistor would usually look as shown and would not have any special property apart from decreasing current. However, there are special resistors made up of semi-conductor material that give these resistors special properties.

SPECIAL RESISTORS:

L.D.R Thermistor

The Light Dependent Resistor (L.D.R):

A Light Dependent Resistor or (L.D.R) is a special resistor whose resistance varies with the amount of ____________________. It is made up of a special semiconductor material (cadmium sulphide). In the dark it has a very high resistance (e.g. 2MΩ) and in sunlight it has a very low resistance (e.g 100Ω). DARK - _______________ resistance SUNLIGHT - _______________ resistance When will the L.D.R conduct more current? _____________________________________________.

Use for an L.D.R: ____________________________________________________

The Thermistor:

A thermistor is a special resistor whose resistance varies with ____________________. When cold, it has a very high resistance, while when hot it has a very low resistance. COLD - _______________ resistance HOT - _______________ resistance When will the thermistor conduct more current? _________________________________________.

Use for a Thermistor: __________________________________________________

fixed resistor



19The Lightmeter

Describe briefly an experiment to find the resistance of a thermistor at 750C

When light falls on the LDR, the milli-ammeter gives a reading because current flows. In the dark, the resistance of the LDR

is__________________, and the current is

__________________.

In sunlight, the resistance of the LDR is

__________________, and the current is

__________________.

The greater the amount of light, the ___________

the current flowing through the circuit.

Method: When the temperature reaches 750C, the voltage is noted on the _______________ and the current is noted on the _______________. Equation: ________________________________ Precaution: ___________________________________________________________________________________________________________________________



20

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