National 4/5

Physics

Gleniffer High School

WAVES

Class Notes

Contents

Units, Prefixes and Scientific Notation

1. SI units

2. Prefixes and Scientific Notation

3. Scientific Notation Practice

4. Converting Numbers

Wave Properties

5. Transverse and Longitudinal Waves

6. Wave Characteristics

7. Wave Speed

8. Frequency

9. Period

10. The Wave Equation

11. Wave Properties Summary

Diffraction

12. Diffraction

Sound

13. The Speed of Sound

14. Waveforms

15. Noise and Decibels

16. Ultrasound and Sonar

Electromagnetic Spectrum

17. Electromagnetic Family

18. Radio waves

19. Microwaves

20. Infrared

21. Visible Light

22. Ultraviolet

23. X-rays

24. Gamma rays

25. EM Spectrum Summary

Refraction

26. Refraction

27. Lenses (uses of refraction)

Reflection

National 5 Data Sheet

Speed of light in materialsSpeed of sound in materials

Material

Speed in m s−1

Air

3·0 108

Carbon dioxide

3·0 108

Diamond

1·2 108

Glass

2·0 108

Glycerol

2·1 108

Water

2·3 108

Gravitational field strengths

Specific heat capacity of materials

Specific latent heat of fusion of materials

Melting and boiling points of materials

Material

Melting point

in oC

Boiling point

in oC

Alcohol

−98

65

Aluminium

660

2470

Copper

1077

2567

Glycerol

18

290

Lead

328

1737

Iron

1537

2737

Specific latent heat of vaporisation of materials

Radiation weighting factors

Type of radiation

Radiation weighting factor

alpha

20

beta

1

fast neutrons

10

gamma

1

slow neutrons

3

X-rays

1

National 5 Relationship Sheet

You might notice that centi- (as in centimetres) is the “odd one out”. It doesn’t follow the pattern!

Can you spot the pattern of the others?

2. Prefixes and Scientific Notation

Often in physics, we are dealing with very small or very large numbers. In order to save ourselves from writing such numbers as 0.0000000001 or 230 000 000, we use prefixes and scientific notation.

1. SI units

There can be many ways of describing a quantity, for example distance: metres, miles, inches, yards etc. To avoid confusion, scientists have decided on using consistent units internationally. This means that when we are doing calculations involving, for example, a distance, we always use metres.

This system is called the International System of Units — SI units for short.

It is important that we always write down the units that we are using, and convert to the

appropriate units when necessary. Here are some SI units we’ll be using:

Units, Prefixes and Scientific Notation

I can...

· use appropriate SI units

· use prefixes: nano (n), micro (μ), milli (m), kilo (k), mega (M), giga (G).

· use scientific notation

REMEMBER:

minutes to seconds

x minutes by 60

hours to seconds

x hours by (60 x 60)

days to seconds

x days by (24 x 60 x 60)

years to seconds

x years by 365 x 24 x 60 x 60

4. Converting Numbers

Kilo or k = x 1000 or x 103Mega or M = x 1 000 000 or x 106

Centi or c = ÷ 100 or x 10-2Mili or m = ÷ 1000 or x 10-3

Example 1. Convert 3.2km into metres

3.2km = 3.2 x 1000 = 3200m or3.2km = 3.2 x 103m

Example 2. Convert 6.2ms into seconds

6.2ms = 6.2 ÷ 1000 = 0.0062sor6.2ms = 6.2 x 10-3s

Practice Questions

1. Convert into metres

a)4km =mor 4 x 10Choose an item.m

b)12.6Mm =mor12.6Choose an item.m

c)5.7cm =mor5.7 Choose an item.m

1. Convert into kilograms (trickier)

a) 4000g =kgor4 Choose an item.kg

b) 0.1Mg=kgor1 Choose an item.kg

c) 5mg =kgor5 Choose an item.kg

1. Convert into seconds

a) 2.2ms =sor2.2 Choose an item.s

b) 720ns=sor7.2 Choose an item.s

c) 0.1ms =sor1 Choose an item.s

3. Scientific Notation Practice

2300000 = 2.3 x 10Choose an item.4560000000 = 4.56 x 10Choose an item.

30000000 = 3 x 10Choose an item.806000 = 8.06 x 10Choose an item.

0.005 = 5 x 10Choose an item.0.0000000047 = 4.7 x 10Choose an item.

5. Transverse and Longitudinal Waves

Waves carry Choose an item.. The substance the wave travels through is known as the

Choose an item..

Transverse:

The particles oscillate (vibrate) at Choose an item. angles to the direction of the wave energy. Examples of transverse waves are Choose an item. and Choose an item. waves.

Longitudinal:

The particles oscillate back and Choose an item. in Choose an item. the direction as the motion of the wave (and the energy).

An example of a longitudinal wave is Choose an item..

Wave Properties

I can...

· state that energy can be transferred as waves

· state the difference between a transverse and a longitudinal wave and give examples of these.

· state the definitions of frequency, period, wavelength, amplitude and wave speed.

· determine the frequency, period, wavelength, amplitude and wave speed for transverse and longitudinal waves.

· do calculations involving d=vt, v=fλ and f=N/t

· do calculations involving T=1/f

Question:

a) what is the wave’s amplitude?

b) what is its wavelength?

Answers:

a) A = 2m

b) λ = 6 metres ÷ 3 waves = 2m

Example 1

Look at this water wave

6. Wave Characteristics

We use the following terms to describe parts of the wave

Choose an item.

Choose an item.

Choose an item.

Choose an item.

Choose an item.

8. Frequency

Example:

What is the frequency if 400 waves are produced in 20s?

N = 400

t = 20s

f = ?

Hz

s

m

s

ms-1

7. Wave Speed

The distance travelled by a wave travelling at a constant speed can be calculated using:

Example:

The crest of a water wave moves a distance of 4m in 10 seconds. Calculate the speed of the wave.

d = 4m

t = 10s

v = ?= 2.5ms-1

The speed of sound in air is 340ms-1 and the speed of light in air is 300 000 000ms-1

(or 3 x 108ms-1). Light travels approximately 1 million times faster than sound!

Hz

s

ms-1

Hz

m

from knowledge

10. The Wave Equation

We can also find the speed of a wave using its frequency and Choose an item..

Example

Microwaves have a frequency of 9.4 GHz. Calculate their wavelength.

v = 3 X 108

f = 9.4 x 109

λ = ?

λ = 0.032m

9. Period

We can consider the case for just one wave. The number of waves is 1 and the time taken is called the Choose an item.. The period is measured in Choose an item.

Also

Example

A certain breed of bat emits ultrasound waves with a period of 23µs. Calculate the frequency of the ultrasound.

T = 23 X 10-6s

f = ?

= 43.5 KhZ

9. Wave Properties Summary

12. Diffraction

All waves will Choose an item. around obstacles placed in their way. This bending effect is called ___________. The longer the wavelength the __________ they diffract.

Example: Choose an item. Choose an item.

A wave with wavelength of 4m will diffract ________ than a wave with wavelength of 2m. A wave of frequency 1000Hz will diffract ________ than a wave of frequency 50Hz. The waves used for TVs are _______ than those used for radios. This is why you might be able to receive radio signals in the shadow of hills, where you wouldn’t get TV signal

NOTE: Diffraction is why we can hear the sound from objects around a corner but cannot see them. Sound waves have a much lower frequency than light waves (or any other part of the electromagnetic spectrum) and so a much longer wavelength.

wavefronts

The wavefronts bend around the object as it passes.

NOTE: The closer the wavefronts are together, the shorter the wavelength (and so higher the frequency of the waves).

DIFFRACTION

12. The Speed of Sound

Sound travels as Choose an item. waves. Sound travels through Choose an item., Choose an item. and Choose an item., but it will not travel through a Choose an item..

Experiment to measure the speed of sound

Connect two microphones to an Choose an item.. Measure the distance between microphones using a Choose an item.. Make a loud Choose an item.. When the sound gets to microphone A the timer Choose an item.. When sound gets to microphone B the timer Choose an item.. Use the Choose an item. between the microphones and the Choose an item. taken by the sound to get from microphone A to microphone B to calculate the speed of sound using:

The speed of sound in air is Choose an item.. The speed of light in air is Choose an item.ms-1. Light is much faster than Choose an item.. In a thunderstorm the lightning and thunder are made at the same Choose an item.. We see the Choose an item. first, because the light waves travel Choose an item. than the sound, so it gets to us first.

SOUND

15. Noise and Decibels

The larger the amplitude the Choose an item. the sound. Sound level or loudness is measured in units called Choose an item. or Choose an item. for short. Normal conversation is Choose an item. dB. Danger level is Choose an item. dB. A loud concert is Choose an item. dB. Loud sounds can damage your Choose an item., so you should wear Choose an item. protectors, such as Choose an item. plugs, ear defenders or noise Choose an item. headphones. Choose an item. is the name we give to any sounds which we don’t want, such as traffic that could cause hearing damage

14. Waveforms

We can display sound waves on an oscilloscope screen. The Choose an item. of a sound wave corresponds to the loudness of the sound. The Choose an item. of the waves corresponds to the pitch of the sound.

Amplifiers can be used to make a sound Choose an item.. This increases the Choose an item., but doesn’t change the Choose an item. of the sound.

16. Ultrasound and Sonar

Humans can hear sound waves with frequencies between Choose an item. and Choose an item.

Hz. Frequencies above 20 000Hz are called Choose an item., and frequencies below 20 Hz are called Choose an item.. Put the two names in the correct boxes on the diagram.

When ultrasound travels from one medium into another some of it Choose an item. back. We can use this fact for medical imagining, such as looking at unborn Choose an item.. We can also use ultrasound to break up Choose an item. stones.

Sonar Choose an item. is used on ships and submarines to detect ______, other vessels, or the seabed. A pulse of Choose an item. is sent out from the ship. It Choose an item. off the seabed or shoal of fish and the echo is detected. We can use the time taken for the sound to travel back to work out the depth. Bats use the same idea to work out their surroundings.

17. Electromagnetic Family

Electromagnetic Choose an item. describes a range, or a family of waves, which all travel at the same speed: Choose an item. x 108 ms-1. This is known as the speed of Choose an item. and is given the symbol c. This is a universal speed limit—NOTHING can travel faster than c. Our eyes are only able to detect one small part of the spectrum (this is the colours that we see).

Here is the full spectrum. Fill in the names of the missing waves.

Radio waves have the longest Choose an item.. Gamma rays have the shortest Choose an item. and therefore the highest Choose an item.. As the frequency of the wave increases the wave has more Choose an item.. This means that Choose an item. have the most energy and Choose an item. waves have the least. In the spectrum the waves which diffract the most are Choose an item. waves, because they have the Choose an item. wavelengths.

THE ELECTROMAGNETIC SPECTRUM

21. Visible Light

This light is made up of a range of different Choose an item.. Red has a Choose an item. wavelength than blue light. A concentrated beam of visible light of one wavelength is called a Choose an item. beam. It can be used in laser eye Choose an item..

20. Infrared

Another name for infrared radiation is Choose an item.. It can be detected by a thermometer. In medicine it can be used in heat treatment of damaged Choose an item. tissue. Rescue services can use Choose an item. imaging cameras to find people in dark or smoky places. The signal between your Choose an item. and TV is also transmitted using infrared waves.

19. Microwaves

Microwaves are used to carry signals up to Choose an item. in space and between our mobile phones! We can also use them to Choose an item. up food in a microwave oven. They are emitted by Choose an item. circuits, and can be detected using an Choose an item., just like radio waves. Microwaves could cause Choose an item., if concentrated.

18. Radio waves

Radio waves have long Choose an item., so they are good at Choose an item. round hills and buildings. This makes them ideal for carrying radio and Choose an item. programmes to your house. Radio waves are emitted by Choose an item. circuits and some stars. They can be detected by using an Choose an item.. Radio waves are safe, in fact there are radio waves passing all around us right now!

24. Gamma Rays

Gamma rays are created in the nuclei of Choose an item., during radioactive decay. Gamma rays can be used to kill Choose an item. cells in your body. Chemicals emitting gamma radiation can also be injected into your Choose an item. stream. A gamma camera picks up the Choose an item. radiation being emitted by the chemicals and creates an image of Choose an item. flow in your body. This is called a radioactive Choose an item.. Overexposure to gamma rays can cause Choose an item.. We can detect gamma rays using a Geiger–Müller tube.

23. X-Rays

X-rays pass through most tissue and cause photographic film to turn Choose an item.. However, X-rays are absorbed by Choose an item. in your body, so the photographic film behind bones stays white, allowing doctors to detect, for example, broken bones. Overexposure to X-rays can cause Choose an item., which is why there is a limit to how many X-rays you can have in one year. X-rays are created when very Choose an item. electrons hit a metal target.

22. Ultraviolet

Most of our ultraviolet radiation comes from the Choose an item.. Too much of it can Choose an item. the skin, or even worse, cause skin Choose an item.. This is why it’s advised to wear sun Choose an item. when outdoors. Special Choose an item. chemicals can be printed on important items, such as money, as Choose an item. markings. These markings only show up under Choose an item. light. Ultraviolet light can be used to treat skin conditions, like Choose an item..

3

25. Electromagnetic Spectrum Summary

Type of Wave

Source

Detector

Approximate Wavelength

Use

Danger of Exposure

Choose an item.

1km – 1m

Choose an item.

1cm (10-2m)

Choose an item.

10µm (10-5m)

Visible Light

~700nm – Red

~550nm - Green

~500nm – Blue

~400nm - Violet

Choose an item.

10nm (10-8m)

Choose an item.

0.1nm (10-10m)

Choose an item.

10pm (10-12m)

Examples

26. Refraction

Refraction is the process where the Choose an item. of a wave changes as it travels from one medium into a different medium (i.e. air into glass).

If the light travels at an angle to the normal from one medium into another then it’s Choose an item. also changes. The frequency of the light does not change.

Here is a diagram showing a beam of light travelling from air into the block then back into air.

Line Q is drawn at Choose an item. to the boundary. It is called the Choose an item.. All angles are measured from the normal to the ray of light.

angle w = angle of Choose an item. angle x = angle of Choose an item.

angle y = angle of Choose an item. angle y = angle of Choose an item.

REFRACTION

NOTE: It is the refraction of white light through raindrops (with a similar shape to a prism) that causes rainbow to be formed.

This effect is used in lenses or prisms as shown below.

As white light (the light we get from the sun) is made up of several different wavelength of light.

Each wavelength refracts be a different amount (red refracts the least and violet refracts the most) and so when white light is passed through a prism, a spectrum is produced.

Above a certain angle of incidence, refraction no longer occurs, and instead the light wave is reflected back into the medium where it came from. This is known as total internal reflection. The minimium angle of incidence that causes the wave to undergo total internal reflection is called the critical angle.

Total internal reflection is used in optical fibres. Optical fibres can be used for communication or in medical applications to allow doctors to see into the body. One bundle of fibres carries light into the body whilst another carries the light back out of the body. This instrument is known as an endoscope.

27. Lenses

Lenses make use of the effect of refraction that causes light to change direction.

When light rays pass through a convex lens they come together (converge). When light rays pass through a concave lens they move apart (diverge). The more curved a lens is the greater the effect on the light rays.

Lenses can be used to correct sight problems

28. Reflection

The law of reflection states that the angle of incidence, i, is equal to the angle of reflection, r. Remember that all angles in a ray diagram are measured from the normal to the line representing the ray (wave).

Reflection from curved mirrors (reflectors)

All waves reflect and if we examine the reflection of light on a curved mirror we can see how they can be used to spread light out or focus it to a point.

Concave reflectors are used to focus light beams to a central focal point. This principle is used for satellite dish receivers on the side of house that collect and focus signals from satellite to a an aerial at the centre of the dish.

Convex reflectors are used to spread light out. You may find these in the corner of small shops, or sharp bends in roads, allowing you to get a clear view around corners.

120000 = 1.2 x 10

5

0.00002 = 2 x 10

-5