introduction to physics(teacher)

7/27/2019 Introduction to Physics(Teacher)

1/24

LEARNING OBJECTIVES

By the end of this lesson you should be able to:

1.1 Understanding physics

* Explain what Physics is

* Recognize the Physics in everyday situations and natural phenomena

1.2 Understanding Base quantities and derived quantities

* Explain what base quantities and derived quantities are

* List base quantities and yheir units* List derived quantities and their units

* Express quantities using prefixes

* Express quantities using scientific notation

* Express derived quantities as well as their units in terms of

base quantities and base units* Solve problems involving conversion of units

1.3 Understanding scalar and vector quantities

* Define scalar and vector quantities

* Give examples of scalar and vector quantities

1.4 Measuring Physical quantities

* Measure physical quantities using appropriate instruments* Explain accuracy, consistency and sensitivity

* Explain types of experimental errors* Use appropriate techniques to reduce errors* Use the vernier calipers and micrometer screw gauge

1.5 Analyzing a scientific investigations

* Identify variables in a given situation

* Identify a question suitable for scientific investigation

* Form a hypothesis* Design and carry out a simple experiment to test the hypothesis

* Record and present data in a suitable form

* Interpret data to draw a conclusion

* Write a report of the investigation.

1


2/24

CHAPTER 1: INTRODUCTION TO PHYSICS

1.1 Understanding Physics

1. Physics is the branch of science concerned with the study ofnatural phenomenaand properties of matter and energy.

2. Name several physics concepts related to daily live or natural phenomenon.

Choose from the list below :

Surface tension Refraction of light Friction Inertia

Resonance Air resistance Density Gravitational force/ radio wave Reflection of light

No. Phenomena Physics concepts

1 A straight stick seems bent in water. Refraction of light

2 Satellites do not fall out of the sky. Gravitational force

3 While a car is braking to a stop, you continue in

motion, sliding along the seat in forward motion.

Inertia

4 More massive object (a stone) falls faster than

less massive object (a feather).

Air resistance

5 People can communicate using mobile phones. Electromagnetic

wave// radio wave

6 We can see the image of an object in a mirror. Reflection of light

7 A submarine can sail on the sea surface and under

the sea.

Density // Upthrust

8 We can walk on a floor without falling. Friction

9 A singer can scatter a glass by singing a certain

note.

Resonance

10 A needle can be made to float on a surface of

water.

Surface tension

2


3/24

3. Fields of study in Physics.

No. Field of study Explanation

1 Force and motion/ Mechanics Investigates the action of force andmotion.

2 Heat Studies of heat on different types ofmatter.

3 Light / Optics Explain the different phenomena due tolight andsight.

4 Waves Understanding the properties of different

types of waves and their users.

5 Electricity and

electromagnetism

Investigate the interaction of electric and

magnetic fields.

6 Electronics Studies the use of electronics devices in

various fields.

7 Nuclear physics Study of nuclear structure and their

application.

4. Importance of physics

(a) There is a close relationship between the study of physics and other sciences,including astronomy, biology, chemistry and geology.

(b) There is a close connection between physics and the practical developments inengineering, medicine and technology .

(c) The application of fundamental laws and theories have enabled engineers andscientists to putsatellites into orbit, receive information from space probes,

and improve telecommunications.

(d) Physics improves the quality of life, i.e. many home appliances function throughthe operation of principles of physics .

1.2 Understanding base quantities and derived quantities.

1. A physicalquantity is a quantity that can be measured. The value of the

measurement consists of a numerical magnitude and a unit.Example:

1. A book with a mass of 2 kg

Physical quantity : massNumerical magnitude/value: 2

Unit of measurement (SI unit) : kg

2. Length of a meter rule is 100 cmPhysical quantity : length

Numerical magnitude/value: 100

Unit of measurement (SI unit) : cm

3


4/24

3. Temperature of boiling water is 100 oC

Physical quantity : TemperatureNumerical magnitude/value: 100

Unit of measurement (SI unit) : oC

The International System of Units, known as SI, is based on the metric

system of measurements.

2. Other examples of physical quantities are velocity, force and time.

3. All physical quantities can be classified into two groups :a) A base quantity is a physical quantity that cannot be defined in terms of

other physical quantities.

A table below shows five base quantities and their respective SI units.

Base quantity Quantity

symbol

SI unit Symbol

Length l metre m

Mass m kilogram kg

Time t second s

Electric current I ampere A

Temperature T kelvin K

b) A derived quantity is a physical quantity which is obtained by combining

base quantities by multiplication, division or both these operations

Derived

quantity

Relationship with the

base quantities

Relationship

with the units

Derived units

Volume, V Length x breadth x height m x m x m m3

Density, Volume

Mass

m

kg kg m-3

Velocity, v

Time

ntDisplaceme

s

m m s-1

Acceleration, a

takentime

velocityofChange

_

__

s

ms m s-2

Momentum Mass x Velocity kg x m s-1- kg m s-1

Force, F Mass x Acceleration kg x m s-2 kg m s-2 (N)

Impulse Change of momentum kg x m s-1 kg m s-1 (Ns)

Energy, E Force x Displacement kg m s-2 x m kg m2 s-2 (J)

Power, P

Time

Energy

s

skgm 22 kg m2 s-3 (W)

4


5/24

4. A value in standard form or scientific notation is a value written in the form of

where

1

A < 10n is an integer (.,-2, -1, 0, 1, 2, .)

Example :

Value Value in standard form

The size of a flu virus 0.000 000 2 m 2.0 x 10-7 m

The equatorial diameter

of earth

12 760 000 m 1.276 x 107 m

5. We useprefixes to simplify the expression of very big or very small numericalvalues of physical quantities. A Prefix is a multiplying factor used to present largeor small value

6.

Prefix Symbol Value

tera T x 1012

giga G x 109

mega M x 106

kilo k x 103

deci d x 10-1

centi c x 10-2

mili m x 10-3micro x 10-6

nano n x 10-9

pico p x 10-12

7. Conversion of units

Example : Convert to SI unit and standard form.

a) 3.4 km = 3.4 x 103 m

= 3400 m

b) 1.5 g cm-3 =3

5.1

cm

g

=36

3

100.1

105.1

mx

kgx

= 1.5 x 10 3 kg m-3

5

Notes :

1 g = 10-3 kg

1 m3 = 106 cm3

1000 g = 1 kg

1 cm3 = 10-6 m3

A x 10 n


6/24

c) 72 km h-1 =h

km

1

72

=sxx

mx

60601

10723

= 20 ms-1

7. Solve problems that involve the conversion of units.Complete the table below with standard form and convert the unit

Quantity Standard form

Scientific notation

Convert to unit

1) 0.000 000 18 Ts 1.8 x 10-7 Ts (1.8 x 10-7 x 1012 )-(-6)

= 1.8 x 10-7 x 1018

= 1.8 x 1011 s

(s)

2) 0.2341 mg 2.34 x 10-1 mg ( 2.34 x 10-1)x 10 -3-(-6)

= 2.34 x 10-1)x 10 -9

= 2.34 x 10-10 Mg

(Mg)

3) 3 854 000 Gm 3.854 x 106 Gm (3.854 x 106) x !09-3

= 3.854 x 106 x !06

= 3.854 x 1012

km

(km)

4) 7 530 nA 7.530 x 103 nA (7.350 x 10 3 ) x 10 -9-(3)

= 7.350 x 10 3 x 10 -6

= 7.350 x 10 -3 mA

(mA)

5) 5 K 5 x 100 K 5 x 100 x 100 (-12)

= 5 x 1012 pK

(pK)

6

Notes :

1 hour = 36000 s1000 m = 1 km


7/24

1.3 Understanding scalar and vector quantities

1. Physical quantities can be classified as scalar quantities and vector quantities.a) Ascalarquantity is a physical quantity which has magnitude only.

Examples : time, length and current

b) A vectorquantity is a physical quantity which has both magnitudeand direction.

Example : Force and velocity

2. Complete the table by choosing the correct physical quantities from the list below.

Length Displacement Velocity Density

Force Current Acceleration TemperatureMomentum Work Weight Time

Distance Speed Energy Depth

Area Volume Mass Power

Scalar quantities Vector quantities

Length Time

Area VolumeDistance Speed

Work Energy

Temperature Density

Mass CurrentDepth Power

Displacement

VelocityForce

Acceleration

Momentum

Weight

7


8/24

1.4 Using appropriate instruments to measure

Recognizing appropriate instruments for measuring.

Choose the appropriate tools to match with the picture given.

Stop watch Micrometer screw gauge Metre rule

Ammeter Vernier callipers Waist watch

Measuring tape Triple beam balance Thermometer

Object Measuring Tools

Temperature ofboiling water

Thermometer

Running TimeStop watch

Book thickness

Vernier callipers

Electric current

Ammeter

Diameter of a wireMicrometer screw gauge

Mass of a key

Triple beam balance

8


9/24

1.4.1 Accuracy

1. Accuracy of a measurement is how close the value of a measurement tothe actualvalue.

2. The level of accuracy is related to the relative error.

3. Relative error =valueActual

Error

_

x 100 %

4. An error is a difference between the measured value and the actual valueor true value .

5. Accuracy can be improved by : -

(a) repeated readings are taken and the average value is calculated

(b) avoid parallax errors(c) avoid zero errors

(d) use measuring instruments with a higher accuracy.

For example, a vernier callipers is more accurate than a ruler .

1.4.2 Consistency

1. Consistency /Precision is the degree of an instrument to record consistentreadings for each measurement by the same way or the ability to record

the same readings when a measurement is repeated.

2. A measurement is considered consistent will have asmallrelativedeviation or no deviation from the average value .

3.. A deviation is a difference between a measurementvalue and its

average value .

4. average deviation =takenvaluesofnumbers

devition

___

5. relative deviation =valueaverage

deviationaverage

_

_

x 100 %

Example:

9


10/24

A student used vernier callipers to measure diameter of a glass rod. The table

below shows the readings.

Measurement Diameter rod (cm) Deviation

1 2.23 0.01

2 2.26 0.02

3 2.24 0.004 2.23 0.02

5 2.25 0.01

Average 2.24 0.012

Relative deviation = %10024.2

012.0

= 0.54 %

6. Consistency can be improved by

(a) eliminating parallax errors(b) exercising greater care and effort when taking readings.

(c) using an instrument which is not defective.

7. Comparisons between consistency and accuracy

a) Consistent but not accurate b) Accurate but not consistent

c) Accurate and consistent d) Not accurate and not consistent.

1.4.3 Sensitivity

10


11/24

1. Sensitivity of an instrument is its ability to detect a small change in the

quantity to be measured.

2. A measuring instrument that has a scale with a smaller divisions is more

sensitive .

3. Measuring instruments.

Measuring

instruments

Smallest magnitude

of quantity (cm)

Sensitivity / Accuracy

Metre rule 0.1 0.1 cm (low)

Vernier callipers 0.01 0.01 cm (moderate)

Micrometre screw

gauge

0.001 0.001 cm (high)

1.4.4 Experimental Error

1. An error is a difference between the true value of a quantity and the value

obtained in measurement .

2. There are two main types of errors :

(a) systematic errors

(b) random errors

3. Systematic errors

- The error in calibration of instrument which makes the instrument

defective.(We must examinethe instrument carefully before using them)

- Zero error which means the pointer of the instrument does not return

to zero when not in use.

( Zero error can be corrected by compensating the readings)

- A problem which persists throughout the experiment such as repeated

error in reaction time and wrong assumption.

- Systematic errors will lead to decrease in accuracy

4. Random errors

11


12/24

- arise from unknown and unpredictable variations in condition, and

will produce a different error every time you repeat the experiment.

- may be due to:(a) personal error ( human limitations of sight and touch )

(b) lack of sensitivity ( instrument does not respond / indicate

insignificant or small change )(c) natural errors ( wind , temperature, humidity, refraction,

magnetic field or gravity )

(d) wrong technique ( applying excessive pressure whenturning a micrometer screw gauge )

- can be minimized by repeating the measurement several times and

taking theaverage (mean) of the reading .

5. Parallax error

- An error in reading a measurement because an observers eye and the

pointer are not in a line perpendicular to the plane of the scale .

(We should place our eyes directlyperpendicularin front of the

pointer or scale of an instrument when taking measurements )

.

1.4.5 Measurement of length

Instrument Example

Measuring tape To measure a waist of a man.

Metre rule To measure the length of a table

Vernier callipers To measure thickness of text book

Micrometre screw

gauge

To measure a diameter of a glass

rod or wire

A. Metre rule

12


13/24

To measure length from a few cm up to 1 m.

1. Precautions to be taken when using a ruler:(a) ensure that the object is in contact with the ruler to avoid

inaccurate readings.

(b) avoid parallax errors(c) avoid zero error and end error.

2. For example: A ruler is to determine the diameter of the wire.

Solution:

Length of wire

Diameter of wire, d = ----------------------------No. of coils

1.5 - 1.0

= -------------------

10

= 0.05 cm

B. Vernier callipers

1. Two pairs of jaws

(a) outside jaws: to measure linear dimensions and outerdiameters(b) inside jaws : to measure innerdiameters

2. Two steel bar scales

(a) the main scale(b) the vernier scale - has a scale on which ten divisions are equal to

nine small divisions on the main scale .

13


14/24

3. Errors in the vernier callipers(a) No zero error

(b) Positive zero error

Positive zero error = + 0.04 cm

(c) Negative zero error

Negative zero error = - ( 1.0 - 0.08 )

= - 0.02 cm

14


15/24

4. For example: Figure below shows the use of a vernier callipers to

measure the size of spherical object. Determine the correct size of

the object if the zero error of the vernier callipers is(a) - 0.08 cm

(b) + 0.08 cm

Example 1 :

(a) Zero error = - 0.08 cmMain scale reading = 2.10 cm

Vernier scale reading = 0.05 cm

Vernier caliper reading = 2 . 1 + 0.05 = 2.15 cm

Correct size of object = vernier caliper reading - zero reading= 2.15 - ( -0.08 ) = 2.23 cm

(b) Correct size of object = 2.15 - ( +0.08 ) = 2. 07 cm

Example 2 :

(a) Zero error = -0.08 cm

Main scale reading = 3.70 cm

Vernier scale reading = 0.04 cmVernier caliper reading = 3.74 cm

Correct size of object = vernier caliper reading - zero reading

= 3.74 (-0.08 ) = 3.82 cm

(b) Correct size of object = 3.74 0.08 = 3.66 cm

15


16/24

C. Micrometer Screw Gauge

1. Comprises of(a) main scale on the sleeve

(b) thimble scale on the thimble

2. Errors in micrometer screw gauge

(a) No zero error

(b) Positive zero error

Correct reading = micrometer reading - ( 0.04 )

(c) Negative zero error

Correct reading = micrometer - ( -0.03 )

16


17/24

Figure below shows a micrometer screw gauge used to measure the size

of an object.

Determine the size of the object if the micrometer has a zero error of(a) + 0.01 mm

(b) - 0.03 mm

Example 1 :

Solution :

The main scale reading = 4.50 mm

The thimble scale reading = 0.21 mm

The reading of the gauge = 4.50 + 0.21 = 4.71 mm

(a) Size of object = the reading of the gauge - zero error

= 4.71 - 0.01= 4.70 mm

(b) Size of object = 4.71 - ( - 0.03 )

= 4.74 mm

Example 2 :

Solution :The main scale reading = 1.00 mm

The thimble scale reading = 0.37 mm

The reading of the gauge = 1.37 mm

(a) Size of object = the reading of the gauge - zero error

= 1.37 0.01= 1.36 mm

(b) Size of object = 1.37 (-0.03)

= 1.40 mm

17


18/24

1.4.6 Measurement of time1. Stop watches are used to measure time interval .

2. Two types of stop watches

(a) The analogue stop watch which is mechanically operated

(b) The digital stop watch which is electronically operated.

1.4.7 Measurement of massThe mass of an object can be measured using a beam balance or an

electronic balance .

1.4.8 Measurement of temperature

1. A thermometer is an instrument used to measure temperature

2. Types of thermometer(a) clinical thermometer

(b) mercury thermometer (range 100C to 1100C with anaccuracy of 10C )

(c) mercury thermometer (range 0 0C to 360 0C with an accuracy

of 2 0C )

3. A mercury thermometer is a sensitive instrument because : -

(a) Mercury is a liquid metal which is sensitive to temperature

changes. It expands and contracts uniformly with thetemperature .

(b) The thin walled glass bulb allows a quick heat transfer

between the heat source and the mercury(c) The capillary tube , which has a small diameter , amplifies a

small expansion in the bulb into a large linear expansion along

the length of the capillary tube .

1.4.9 Measurement of electric current and voltage

Ammeter

1. An instrument used to measure the amount of electric current

flowing through a particular point in an electrical circuit .

2. The SI unit for current is Ampere, A

3. For a small current , a milliammeter is used ( an accuracy of0.1 mA or 0.2 mA is used )

4. It is usually connected in series in an electrical circuit .

18


19/24

Voltmeter1. An instrument used to measure the potential difference ( voltage )

between any two points in an electrical circuit2. The SI unit for potential difference is volt, V.

3. It is connected in parallel in an electrical circuit .

1.5 Analysing scientific investigations

1. The following processes are involved in scientific investigations.

a) A scientific investigation begins with observation. When observing we

come out some questions.. (i.e : hearing, smelling, touching, tasting,

seeing)

b) Making inference is a early assessment or explanation that iscarried out to answer the question raised.Inference is an early conclusion to what we observed

b) Form a hypothesis which is the statement of relationship between

the manipulated variable and the responding variable we would expect.

c) Aim has to be stated so that all the investigating effort is centred

on the main subject.

d) Identify all the variables ;

i ) Manipulated variable is a quantity we manipulate /variable which causes other secondary variables to change.

ii) Responding variable is the quantity which is affected by the

manipulated variable and is measured experimentally.iii) Fixed variable is the quantity that does not change

throughout the experiment.

e) Apparatus / Materials needed to be listed according its specification

19


20/24

example measuring instrument to ensure the success the experiment.

f) Procedure is the sequence of action or operation in order to carry outthe experiment according to the instructions given.

g) Observation is the listing and tabulation of all data obtained in theexperiment.

h) Analysing of data can be carried out by plotting thegraph,followed by the interpretation of graph or calculation to obtain the

required value.

i) Discussion needs to be stated to find out whether the result obtainedsupport the stated hypothesis. Precautions of the experiment can be

suggested to overcome the weakness, to reduce the experimental

error or to improve the result of the experiment.

j) A conclusion is stated concerning the result of the experiment

(is written in accordance with the aim of the experiment and basedon graph). By comparing with the aim stated, this will determine

whether the hypothesis is accepted or rejected.

2. Example : A simple pendulum

1. Inference : When the length of a simple pendulum increases,the period of oscillation also increases. // The period of

pendulum is affected by the length of the thread.

2. Hypothesis : The longer the length of a simple pendulum,

the longer will be the period of oscillation//

3. Aim : To find the relationship between the length of a simple

pendulum and the period of oscillation.

4. Variable :

a) Manipulated variable : Length, lb) Responding variable : Period, T.

c) Fixed variable : Mass of pendulum bob. m

5. Materials : Retort stand, pendulum bob, thread, metre rule, stop watch.

20


21/24

6. Figure

7. Procedure :a) Set up the apparatus as shown in Figure above.// A small brass or bob

was attached to the thread. The thread was held by a clamp of a the

retort stand.

b) The length of the thread , lwas measured by a metre rule, starting with

90.0 cm. The bob of the pendulum was displaced and released.

c) The time for 20 complete oscillations, t was taken using the stop

watch. Calculate the period of oscillation by using, T =20

t

d) The experiment was repeated using different lengths such as 80.0 cm.70.0 cm, 60.0 cm, 50.0 cm and 40.0 cm.

8. Observation / Tabulate data

Length ofstring, l /cm

Time taken for 10oscillation, t (s)

Period ofoscillation

T =20

t(s)

T2

(s2 )

t 1 t 2 Average, t

40.0

50.060.070.0

80.0

90.0

25.2

28.131.033.5

35.7

38.2

25.1

28.231.033.6

35.9

37.9

25.2

28.231.033.6

35.8

38.1

1.26

1.411.551.68

1.79

1.91

1.59

1.992.402.82

3.20

3.65

thread

bob

Retort

stand

21


22/24

Notes :

Symbols and their respective units should be written in the table

A readings of length of string should be written in one decimal place

This is because the metre rule used to measure the length of string can measure

accuracy to 0.1 cm

All sets of readings recorded must be consistent. For example, all reading

time taken, t are recorded in one decimal place.

Average values for t are taken to minimize errors

If the time taken for 20 oscillations is 38.1 s,

Then the period of oscillation, T =20

t=

20

1.38= 1.91 s

T2 = (1.91)2 = 3.65 s2

9. Analysing : Plotting the graph

T2 (s2) against l (cm)T2

(s2 )

l(cm)

x

xx

xx

x

22


23/24

Notes :

a) Plotting the graph

The graph should be labeled by a heading

All axes should be labeled with quantities and their respective units.

The manipulated variable (l) should be plotted on the x-axis while the

responding variable (T2 ) should be plotted on the y-axis

Odd scales such as 1:3, 1:7 , 1:9 0r 1 :11should avoided in plotting graph.

Make sure that the transference of data from the table to the graph is accurate.

Draw the best straight line

- the line that passes through most of the points plotted such that isbalanced by the number of points above and below the straight line.

make sure that the size of the graph is large enough, which is, not less than

half the size of the graph paper or.( > 8 cm x 10 cm )

b) Calculate the gradient

The triangle drawn to calculate the gradient of the graph should not be less thanhalf size of the graph drawn or ( .> 6 cm x 8 cm )

Calculate the gradient using the formula

Put the unit

10. Discussion / Precaution of the experiment / to improve the accuracy

a) The bob of the pendulum was displaced with a small angle

b) The amplitude of the oscillation of a simple pendulum is small.

c) The simple pendulum oscillate in a vertical plane only.

d) Switch off the fan to reduce the air resistance

11. Conclusion

The length of simple pendulum is directly proportional to

the square of the period of oscillation. //

T2 is directly proportional to l (the straight line graph passing through the origin)

23


24/24

introduction to physics(teacher)

Documents