As Physics Practical Set 1 Updated April 2014

7/26/2019 As Physics Practical Set 1 Updated April 2014

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TAYLOR’S COLLEGE SUBANG JAYA

CAMBRIDGE A LEVEL

PHYSICS PRACTICALS

SET 1

FOR INTERNAL USE ONLY

Name : ………………………………….…

Class : ……………………………………

Intake : ………………………………….…

Lecturer : ……………………………………



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PHYSICS PRACTICAL

Experiments A1 - A18

Code: 9702/31 or 9702/32

Instruction to candidates

You are expected to record all your observations as soon as these observations are made, and to

plan the presentation of the records so that it is not necessary to make a fair copy of them. The

working of the answers is to be handed in.

Details on the question paper should not be repeated in the answer, nor is the theory of the

experiment required unless specifically asked for. You should, however, record any special

precautions you take and any particular features of your method of going about the experiment.

Marks are mainly given for a clear record of the observations actually made, for their suitability

and accuracy, and for the use made of them.

Provision has been made in the question paper for you to record your observations and readings

and for you to plot the graphs required. Additional answer papers and graphs should only be

submitted if it becomes necessary to do so.



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List of experiments A1 - A18

A1 Introductory experiment Set 1 p 4

A2 Introductory experiment Set 2 p 9

A3 Triangle of forces board p 13

A4 Determination of acceleration due to gravity by a simple pendulum method p18

A5 To investigate the oscillation of a piece of card which you will first cut to

shape. p 22

A6 (i) Finding the mass of a metre rule using the principle of moments(ii) Finding the densities of different materials p 27

A7 Hooke’s Law p 35

A8 Optics - Determination of focal length p 40

A9 Equilibrium of a suspended mass (June 05) p 47

A10 To make measurements to check the suggested relationship p 53

A11 To compare the temperature of a water bath, measured with a mercury p 57

in glass thermometer (temperature measured using a thermistor)

A12 The relationship between potential difference and current in a resistor. p 61

A13 Resistivity p 68

A14 (i) To find the e.m.f. and internal resistance of a dry cell

(ii) The value of the external resistor at which the power dissipated in it is a

maximum p 72

A15 Potential divider p 80

A16 To determine the resistance of a voltmeter by a simple graphical method p 87

A17 Compound pendulum p 91

A18 Investigate the position of a wooden rod suspended in water as the depth of

water varies (Nov 2009 Paper 31) p 95



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Experiment A1: Introductory Experiment Set 1

Apparatus requirements

1. 30 cm plastic rule

practical manual book

2. vernier caliper

micrometer screw gauge

3. pendulum bob

50 cm thread

stopwatch

retort stand, clamp, boss

wooden block

4. measuring cylinder 50 cm3

pendulum bob

triple beam balance

30 cm thread

set square

30 cm plastic rule

5. micrometer screw gauge

copper wire s.w.g 22



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1. Determine the length l and width w of your lab manual book with a 30 cm plastic rule.

Present your measurements together with their absolute uncertainties.

Reading 1 2 averagel ____ / cm

w ____/ cm

(a) Calculate the % uncertainty in (i) l and (ii) w as follows:

(l and w are the uncertainties in l and w respectively).

(i) % uncertainty in l = 100 xl

lδ%

=

(ii) % uncertainty in w = 100 xw

wδ%

=

(b) Compare and comment on their % uncertainties.

Compare: ……………………………………………………………………...........

………………………………………………………………………………………

………………………………………………………………………………………

Comment: …………………………………………………………………….........

………………………………………………………………………………………

………………………………………………………………………………………



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2. Measure the thickness t of your lab manual book, first with a pair of vernier calipers then with a

micrometer screw gauge. Present your measurements together with their absolute uncertainties.

reading 1 2 3 averagevernier, t ___/cm

micrometer, t ___/mm

(a) Calculate the % uncertainty in t when using (i) vernier caliper and (ii) micrometer screw

gauge as follows:

(i) For vernier caliper: % uncertainty in t = 100 xt

t δ%

=

(ii) For micrometer screw gauge: % uncertainty in t = 100 xt

t δ%

=

(b) Compare and comment on their % uncertainties.

Compare: ……………………………………………………………………...........

………………………………………………………………………………………

………………………………………………………………………………………

Comment: …………………………………………………………………….........

………………………………………………………………………………………

………………………………………………………………………………………



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3. A pendulum bob of length 50 cm is hung from a pivot clamped by two wooden blocks.

Determine the period of oscillations of the pendulum. The period, T , is the time for one

complete oscillation. Present your measurements together with their absolute uncertainties.

l ___/cm No of

oscillations, N

time for N oscillations, t ___ /s period, T / s

(= N

st / )t 1 t 2 mean, <t /s>

4. The density ρ of an object or material is defined as mass/volume.

Determine the density ρ of a pendulum bob provided together with its absolute uncertainty

using the water displacement method.

(a) Volume before V 1 = ( ) cm3

Volume after V 2 = ( ) cm3

Volume V of pendulum bob, V = V 2 - V 1 = ( ) cm3

(Note: Record the uncertainties V 1 and V 2 to ½ of the smallest division on the

measuring cylinder. For subtraction, add the absolute uncertainties. If the uncertainties

in V 1 and V 2 are both V, the uncertainty in V = V + V = 2 V)

Mass m of pendulum bob = ( ) g

Density ρ =V

m= g cm

-3

b. Given that the % uncertainty in ρ = % uncertainty in m + % uncertainty in V ,

calculate the absolute uncertainty in (i) the % uncertainties in ρ (ii) the absolute

uncertainty in ρ as follows:

(i) % uncertainty in m = ±

(ii) % uncertainty in V = ±

(iii) % uncertainty in ρ, 100 xρ

δρ= (i) + (ii) = ±



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(iv) Absolute uncertainty in ρ, δρ = ±

[δρ =100

yuncertaint%x ρ ]

c. Hence, density ρ = ( ± ) g cm-3

d. What measurement would you improve in order to increase the precision of the density

measurement?

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5. Measure the diameter of the copper wire provided five (5) times along the length

of the wire and in different directions. Calculate the percentage uncertainty of the

diameter.

1 2 3 4 5 average

d ___ / mm

(a) Mean diameter d =

(b) % uncertainty in d = d

d δx 100 %

=



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Experiment A2: Introductory Experiment Set 2


1. retort stand, boss, clamphelical spring

mass 50 g

mass hanger 20 g

2. voltmeter (5 V)

ammeter (0 – 1 A)

connecting leads

constantan wire s.w.g 28, 60 cm

dry cells, 2 pieces

battery holder

micrometer screw gaugemeter rule

3. stopwatch

plasticine

meter rule

newspaper



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1. A helical spring with a mass at one end is hung from a clamp. You are to add another mass

unto it and measure the new extension. Draw a diagram to show how you obtain the

extension and present your measurements together with their absolute uncertainties.

Diagram Measurements

Position before mass added = ___ ___ cm

Position after mass added = ___ ___ cm

Extension = ___ ___ cm

2. Connect the circuit below as shown.

a. Obtain the readings of the voltmeter and ammeter together with their uncertainties. You may

record the uncertainties to ½ of the smallest division of the scale on the instruments.

1 2 Average V / V

V / V

I / A

b. Resistance of wire is given by I

V R

(i) Calculate the resistance R of the wire.

V

bare wirex Y

A



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(ii) Calculate the absolute uncertainty in R as follows:

% uncertainty in V = %100V

V δ=

% uncertainty in I = %100 I

I δ

=

% uncertainty in R = % uncertainty in V + % uncertainty in I

=

Absolute uncertainty in R =

c. Hence resistance R = ( )

d. The resistivity ρ of the wire is given by A

l R

ρ where A is the cross sectional area of

wire and l is the length of wire.

(i) Length of wire l = ( ) cm

% uncertainty in l =

(ii) Diameter of wire d =

(take 5 readings and take average)

% uncertainty in d =

Cross-sectional area A = 2

4

1d π =

% uncertainty in A = 2 x % uncertainty in d =



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(iii) Calculate the resistivity of the wire using the relationship =l

RA.

Resistivity =

Given that the % uncertainty in ρ= % uncertainty in R + % uncertainty in A + % uncertainty in l

=

Hence, absolute uncertainty in the resistivity =

Hence resistivity of wire = ( ) m

3. Determine the acceleration g of free fall using a lump of plasticine and the following equation,

h = ½ g t 2

where h = height of building from which the object is released

t = time taken for the object to fall through this distance/height

Method: Let an object fall from rest from the highest point you can attain and measure thetime taken for it to fall.

Height h fallen = ( ) m

1 2 3 4 5 average t /s

t ___ / s

Given that the % uncertainty in g = 2 x (% uncertainty in t ) + % uncertainty in h, determine

the acceleration g of free fall together with its absolute uncertainty.

g = ( )



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Experiment A3: Triangle of Forces Board


1 Three different objects of unknown weight. The weights of the objects are between

0.5 N and 5.0 N.

2 Two 1.0 N weight hangers and six 1.0 N slotted weights.

3 Three A4 sized sheets of white paper.

4 Strong wooden board, about 50 cm × 50 cm.

5 Two stands, two bosses and two clamps. These are to hold the board securely in

a vertical position.

6 Two pulleys. These need to be able to be clamped to the top corners of the board.

7 Blu-tack to attach the sheets of paper to the board.

8 Three pieces of strong thread, each about 50 cm long.



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In this experiment you will be using a vector triangle to find the weight of an object.

Theory

It is possible to represent and calculate an unknown force using a vector diagram. If a three force

system is in equilibrium, then the resultant force is zero and so the force vectors can berepresented as a complete triangle. By knowing two of the forces and the angles between them, it

is possible to draw a scale diagram and to measure calculate the third force from the diagram.

You will be using this principle to find the weight of various objects in a system in equilibrium.

Making measurements and observations

1 Take three equal lengths of thread, each around 0.5 m long. Tie their ends together so that they

form a Y shape.

2 Tie one of the objects of unknown weight to the end of one thread and tie a small loop in eachend of the other two threads.

3 Clamp the board in a vertical position. Clamp the two pulleys to the large stiff board, one on

each side near to the top. The arrangement should be such that the pulleys are between 0.4 m

and 0.7 m apart.

4 Attach a clean sheet of white paper to the board behind the pulleys.

5 Loop the two threads with loops over the pulleys and add weights to the end until the object in

the middle is supported. The two weights and the object of unknown weight must be in

equilibrium. You may need to increase or decrease the weights on each side in order to achieve

equilibrium. The arrangement is shown in the diagram below.

6 Record the two weights, making a note of which side of the board they are on.

7 Trace the lines of the three threads onto the paper on the board. It is very important that you are

able to record the angles between the lines accurately. You may find it easier to put dots on the

paper behind the threads and then join them up when the paper is removed.

8 Repeat the experiment again for each of the objects of unknown weight.



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force B

unknown

weight

force A

unknown

weight

(to scale)

force B

(to scale)

force A

(to scale)

Recording and presenting your data

1 For each object of unknown weight, your results will be the sheet of paper from the forces

board.

2 From the lines drawn on the piece of paper, measure the angles between the threads.

3 Construct a triangle of forces. Begin by drawing the two known forces, starting the second

force at the end of the arrow representing the first one. The force arrows must have the correct

angle between them. You will need to decide on an appropriate scale to use (e.g. 5 cm =1 N):

the scale you use will depend upon the weights used.

4 Connect the point at the start of the first force arrow and the point at the end of the second force

arrow with a third arrow. The diagram below shows an example of how the lines on the paper

are turned into a force triangle.

5 Repeat 1 – 4 to obtain vector diagrams for each of the objects of unknown weight.

Space for vector diagrams (If the space provided is not sufficient, you may attach additional A4

size papers).



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Analysing your data

1 Measure the force arrows representing the weight of each the objects of unknown weight.

2 Use the scale to calculate each of the unknown weights.

Evaluation

1 Ask the teacher for the actual weights of the objects. Write a paragraph comparing your results

with the actual weights, commenting on the reasons for the differences.

……………………………………………………………………………………………………..

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Extension work (Optional)

Suspend two weights each of 5.0 N from the threads that pass over the pulleys. Investigate the

relationship between the angle between these two threads and the weight suspended from the

central thread.



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Experiment A4: Determination of Acceleration due to Gravity by a Simple Pendulum

Method


1. thread (110 cm)

2. stop watch

3. metre-rule

4. retort stand and clamp

5. two pieces of wooden blocks

6. pendulum bob



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The periodic time T of a simple pendulum, for small angle of swing, is related to its length l and

the acceleration due to gravity g at the place of location of the pendulum by the formula

T = 2g

l

In this experiment, you are to determine the value of g at your laboratory by means of the simple

pendulum.

Fig. 4

Instructions and Information

1. Set up the apparatus as shown in the diagram.

2. How should l be measured? Draw a diagram if it helps to explain.

…………………………………………………………….………………………………………

…………………………………………………………….………………………………………

3. Through what angle should the pendulum bob be swung?

…………………………………………………………….………………………………………

l



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4. (i) Draw a table showing l / cm, t / s, T / s and T 2 / s

2.

(ii) Justify the significant figures you have recorded for values of T and T 2.

…………………………………………………….………………………………………

…………………………………………………….………………………………………

5. Plot an appropriate graph on the graph paper provided. Calculate a value for g from the slope.

State its units.

6. If the bob is of a different size(mass) but l is the same, state and explain the effect on the value

of T .

………………………………..………………………….………………………………………

………………………………..………………………….………………………………………



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Experiment A5: To Investigate the Oscillation of a Piece of Card which you will first cut to

shape


1. card; A4 size

2. scissors

3. stopwatch

4. half-metre rule

5. plumbline

6. pin

7. stand, boss and clamp

8. carbon paper (A4)



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(a) Find the outline of an ellipse in this experiment and use the outline as a pattern to draw a

copy of the ellipse onto the given sheet of card. Make sure that you transfer the line PQ

marked on the pattern. Cut out the cardboard ellipse.

(b) Using the plumb-line and whatever else you wish from the apparatus provided, locate the

center of gravity of the ellipse and label it R. If R does not fall on the line PQ, move theline PQ so that it runs through R.

(c) The ellipse is to be pivoted from a series of holes along the line PQ so that it makes small

oscillations in its own plane. You are to investigate the relationship between the period T

of these oscillations and x, the distance of the pivot from R.

Record your readings, including a column for x2

and T 2 x with their appropriate

units.

Justify the significant figures you have recorded for the values of x2

and T 2 x.

……………………………………………………………….…………………………….

……………………………………………………………………………..……………….

……………………………………………………………….…………………………….

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(d) Theory suggests that

T 2 x = m x

2+ c

where m and c are constants. Plot a straight line graph to test this relationship,

and hence determine values for m and c.

(e) The finite size of the pivoting hole in the ellipse and the marking of the point R mean that

the distance x is not clearly defined in part (c) above. Outline ways in which the

measurement x could be made to be as accurate and reliable as possible.

………………………………..……………………….………………………………………

…………………………………..…………………….………………………………………

……………………………………..………………….………………………………………

(f) Attach the ellipse in your book.

Determination of m

Determination of c



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Q

P



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Experiment A6:

(i) Finding the Mass of a Metre Rule using the Principle of Moments


1 Stand, boss and clamp. The bar of the clamp needs to be long enough to balance a

metre ruler on.

2 Meter rule. This should be quite stiff. Wooden metre rules are preferable as plastic

ones can bend.

3 Loop of thread long enough to fit loosely around the metre rule.

4 20 g mass hanger and five 20 g slotted masses.

(ii) Finding the densities of different materials


1 Sheet of paper. A sheet of A4 writing paper.

3 Six identical glass marbles.

4 Blu-tack.

5 Two set squares.

6 Metre rule.

7 30 cm rule.

8 Knife edge. This can be a glass prism or any other edge that can be placed on atable and have a metre rule balanced on it.

9 50 g mass.

10 10 g mass.

11 Micrometer screw gauge.

In this experiment you will use the principle of moments, together with the idea of the centre of

gravity, to find the mass of a metre rule.



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Theory

The centre of gravity of a body is a point through which the weight of the body is considered to

act, or appears to act. A metre rule has a uniform shape and a constant density and so the centre of

gravity will be a point exactly in the middle of the rule (at the 50 cm mark).

The principle of moments states that an object is in equilibrium if the sum of all anticlockwisemoments about the pivot is equal to the sum of all clockwise moments about the same pivot.

If a metre rule is balanced horizontally at any point, this means that the clockwise moments and

the anticlockwise moments must be equal.

The arrangement for the experiment is shown in the diagram below.

In this situation, the weight F 1 of the masses provides the anticlockwise moment and the weight

F 2 of the rule provides the clockwise moment. The weight of the rule acts through the centre of

gravity at the middle of the rule. This is shown in the diagram below.

If the rule is balanced, we can apply the principle of moments. This results in the equation

F 1 d 1 = F 2 d 2

where d 1 is the distance between the hanging mass and the pivot and d 2 is the distance between

the pivot and the centre of gravity of the rule. This equation can be rewritten as

m1 g d 1 = m2 g d 2

where m1 is the mass hanging from the rule, m2 is the mass of the metre rule and g is the

pivot(the bar of a

clamp)

metre rule

Masses on hanger

attached to thread

loop

F 1 F 2

d 1d 2

anticlockwise

moment

clockwise

moment



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acceleration of free fall.

This can be rearranged to give

m2 = m1 ×2

1

d

d


1 Set up the stand, boss and clamp so that the bar of the clamp is horizontal and its height above

the bench is a few centimetres more than the length of the mass hanger.

2 Hook the thread loop over the zero end of the metre rule.

3 Hang the mass hanger from the bottom of the thread loop underneath the metre rule.

4 Slide the thread loop so that it is at the 1 cm mark of the metre rule.

5 Move the metre rule and the hanging masses so that the metre rule balances horizontally on the

bar of the clamp stand. (This may be a bit fiddly, so be patient.)

6 When it is balanced, record m1, d 1 and d 2.

7 Repeat the experiment for a total of six different values of m1.


1 All your measurements should be recorded in a table of results. Your table of results should

include a column for m2.

2 The values in the column for m2 should be calculated using the equation

m2 = m1 ×2

1

d

d

Tabulation



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Analysing your data

1 Calculate the average of your values for the mass m2 of the metre rule.

Evaluation

1 Estimate as to the actual uncertainty in each measurement you have taken.

uncertainty in m1 =

uncertainty in d 1 =

uncertainty in d 2 =

2 Describe any steps you took to reduce experimental errors.

…………………………………………………….……………………………………………....

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3 Describe any limitations or problems with the method used to find m2 in this experiment.

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4 Suggest ways in which the accuracy of the measurements taken could be improved.

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……………………………………………………….……………………………………………

…………………………………………………….……………………………………………....

……………………………………………………….……………………………………………

(ii) Finding the Densities of Different Materials

In this experiment you will find the densities of two materials, using the principle of

moments in your measurements of mass.

Theory

The density ρ of a material is usually measured in kg m-3

and is related to the mass m and

volume V of an object made from the material by the equation

ρ =V

m

In this experiment you will determine the densities of two materials from measurements of two

objects, as shown in the table.

material object

glass marble

paper sheet of paper

The masses of the objects will be determined using a simple balance and the principle of

moments. The balance is constructed from a metre rule, a knife edge and a 50 g mass.

These are arranged as shown in the diagram.

Without the 50 g mass or the object of unknown mass, the metre rule is balanced on the knife

edge. Without changing the position of the knife edge under the rule, the 50 g mass and the

objects are placed on the rule and their positions are adjusted until the rule balances.

d 1d 2

object of

unknown mass



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From the principle of moments, it can be shown that

m1 d 1 = m2 d 2

where m1 = 50 g, m2 is the unknown mass, d 1 is the distance from the pivot to the centre of the 50

g mass and d 2 is the distance from the pivot to the centre of the unknown mass.Making measurements and observations

1 Use the 30 cm rule to measure the length and width of the sheet of paper. You should repeat

your readings at different points and average the results.

2 Fold the sheet of paper in half several times. Make a note of how many layers are in the

folded sheet.

3 Use the micrometer screw gauge to measure the thickness of the folded sheet. Repeat your

readings at different points and average the results.

total thickness of N sheets of paper =

4 Use your answers in 2 and 3 to calculate the thickness of a single sheet of paper.

Thickness of a single sheet of paper =

5 Arrange the glass marbles in a straight line and touching each other, as shown in the diagram.

6 Use the two set squares and the 30 cm rule to measure the length of the row of marbles.

length = cm ( 1 d.p.)

7 Divide your answer to 6 by the number of marbles to obtain the average diameter.

diameter = cm (2 d.p.)

8 Divide this figure by two to obtain the average radius r of the marbles.

radius = cm (2 d.p.)



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9 Balance the metre rule on top of the knife edge. Make a note of the position of the knife edge

on the scale of the metre rule.

position =

10 Measure and record the distances d 1 and d 2.

12 Repeat 9 and 10 for each object. You may need to use a smaller mass for the paper.

.


1 For each object, record all the measurements you have made in a clear way, including the

calculation of density. You will need to think about how you lay your work out before you start

taking measurements.

Analysing your data

1 Calculate the mass m2 of each object using the equation

m1 d 1 = m2 d 2.

2 Calculate the volume V of each object. For the glass marble, use the equation

V = 3

3

4r π

where r is the radius of the sphere.



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3 Calculate the density ρ of the material from which each object is made, using the equation

ρ =V

m

density of paper =

density of glass marble =

Evaluation

1 Suggest, with a reason, the measurement that was the largest source of error in the

calculation of the density for each object.

……………………………………………………………………………………………....

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2 Suggest ways in which the accuracy of the experiment could

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Experiment A7: Hooke’s Law

Aims(1) To verify Hooke’s law using a spiral spring

(2) To investigate how the spring constant varies with the arrangement of springs.

Apparatus:

1. One long spiral spring labelled S.

2. Five spiral identical springs (short ones)- spring constant of each spring is labelled.

3. Six slotted masses up to 300 g, each 50 g.

4. Mass holder 50 g

5. One Retort stand, two bosses and two clamps

6. One half-metre rule

7. Three small sticks with holes (for parallel springs)

Pre-Lab Exercise

1. State Hooke’s law.

………………..………….……...………………..………………..………………..……………

….…………..…………..….…...………………..………………..………………..…………[2]

2. State what happens when the proportionality limit is exceeded.

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………………..………………..…..………………..………………..………………..………[1]

3. If the load attached to a vertical spring is doubled, what happens to the extension?

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…..…………..……………….…...………………..………………..………………..…………[2]

4. What graph would you draw to confirm Hooke’s law, and why?

..………………..……………….…..……………..………………..………………..……………

..………………..……………….…..……………..………………..………………..……………

..………………..………………..…..………………..………………..…..…………..………[3]

5. Define spring constant (or elastic constant).

……..…………..……………….…..……………..………………..………………..……………

………………..…………………....………………..………………..………………..………[1]

6. What mechanical property of spring is revealed by the value of the spring constant?

…….………..…………………….…………..………………..………………..……………[1]



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7. If N number of identical springs, each of spring constant k , are connected in series or in

parallel, describe how the spring constant for the system is affected by the type of

arrangement.

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………………..……...……………..……………..………………..………………..……………

………………..……...……………..……………..………………..………………..……………

………………..…….………….…..………………..………………..………………..………[4]

Procedure

1. Design an experiment (need not to write out) to verify Hooke’s law and to determine the

spring constant of the spring S, using the apparatus provided.

Identify the independent and dependent variables in the experiment.

………………..……...……………..……………..………………..………………..……………

Diagram:

Carry out the experiment and tabulate the appropriate readings.



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Analysis

1. Determine the spring constant of one spring.

Details:

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2. Carry out an experiment using a fixed mass of a certain value, three short springs and any of

the given apparatus to find out how the spring constant k varies when the three springs are in

(a) series (b) parallel. You need only to tabulate readings taken and hence calculate the new

spring constant for each arrangement. (choose three with similar spring constants)



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3. How are the spring constant k for each arrangement in part (2) related to the average? Provide

a simple explanation.

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…………..….………………..………………..………………..………………..………………..

………………………………..………………..…………..………………..……………….…[2]

4. If two springs in series are connected in series to the system of three springs in parallel, how

do you think the new k will be in terms of the average?

……………..………………………..………..………………..………………..………………..

……………..………………………..………..………………..………………..………………..

……………...………………………..………..…………..………………..……………….…[2]

5. Perform an experiment to verify your results in part (4). Compare & comment on your results.

Readings

…….……..…………………..………………..………………..………………..………………..

…….……..…………………..………………..………………..………………..………………..

…………...…………………..………………..…………..………………..……………….…[2]

Post-Lab Exercise

1. A spring of spring constant k extends by x when a force of F acts on it.

(a) Show that the elastic potential energy stored in the above-mentioned spring is given by

½ k x2. State one assumption made.

…….……..…………………..………………..………………..………………..…………….

…….……..…………………..………………..………………..………………..…………….

…….……..…………………..………………..………………..………………..…………….

…………...…………………..………………..…………..………………..……………....[3]

(b) Five identical springs mentioned above are connected in such a way that two springs in

parallel are attached in series to a system of three springs in parallel. Determine the total

elastic potential energy stored in the arrangement in terms of k and x.

[2]



40

Experiment A8: Optics - Determination of Focal Length


1. lamp, 12V, 36 W

2. Power supply unit, 12 V

3. Rigid cardboard with a triangular translucent aperture as object

4. Converging lens

5. Lens holder

5. Plasticine

6. Metre rule

7. White screen

8. 2 long connecting leads



41

1. Objectives:

You are to determine the focal length of a converging lens using 2 methods as described in

section 3 and section 4 below.

2. You need to know the approximate value of focal length f . Use a distant object method to

find it. You may need to go out of the lab to get a far-away object.Sketch a ray diagram to illustrate your method.

3. Method 1 (magnification method)

(a) Theory:(i) The magnification of a lens is defined as the ratio of the size of the image to that of the object.

Magnification m =o

I

h

h, where hI is the height of the image and ho is the height of the object.

(ii) The object distance u, the image distance v and the focal length f of a thin lens is given by the

relationship

f vu

111 .

Multiply both sides of the equation by u,

f

u

v

u1

Since the magnification m of the lens is also given byu

v,

1 +m

1=

f

u.

Multiply both sides of the equation by f and rearranging,

f m

f u 1



42

If a graph of u againstm

1is plotted, the graph should be a straight line with gradient = f and the

y-intercept = f .

(b) The triangular aperture on the cardboard acts as the illuminated object. There should be atranslucent paper attached to it. See your teacher if it is not there.

Measure the vertical height ho of the aperture.

height of aperture ho = ………………… cm

(c) Set up the apparatus as shown in Fig. 8.

(d) Place the lens vertically at a distance about 1.3 f from the aperture. Move the screen to the

position where a sharp, inverted image of the triangular aperture is formed. If you fail to

obtain the image, increase your object distance u and move your screen further away.

Ensure that the aperture, the centre of the lens and the screen are in a straight line.

You may request your lecturer to darken the room.

(e) (i) Measure the height hI of the image, and calculate the value of the magnification m using

the relationship m =o

I

h

h.

(ii) Record also the object distance u and the image distance v.

(iii) Repeat the experiment for 5 sets of values of u between 1.3 f and 3 f .

vu

Cardboard

with aperture

lamp

screen

lens

Fig. 8



43

(f) Tabulate your observations. You should include the value u, v, hI , m andm

1in your

tabulation.

(g) Tabulation.

(h) (i) Plot a graph of u againstm

1.

(ii) From your graph, determine its gradient and its y-intercept.

gradient = …………………….

y-intercept = …………………

(iii) Hence determine the average value of the focal length f of the lens.

focal length, f = ………………. cm



44



45

4. Method 2 (graph of image distance v against object distance u)

(a) Theory

From the equation f vu

111 , a graph of v against u is a curve.

If u = v, we have f u

112 or

f v

112

Hence f =2

uor f =

2

v

(b)(i) From the tabulation in method 1 above, tabulate the values of u and v once more.

(ii) Because the path of light is reversible, each observation can give you two records in this

table.

For example, if u = 15.0 cm and v = 30.0 cm, you can also put u = 30.0 cm and v =

15.0 cm.

Hence for 5 set of observations, you will get 10 sets of readings in your table.

(c) Tabulation

(d) On the next page, plot a graph of v against u. If you use the same scale for v and u, the

graph should be symmetrical about the line v = u.

(e)(i) On the same graph, draw a straight line v = u to cut the curve mentioned in (d).

(ii) Hence, deduce 2 values of the focal length f of the lens, and find its average value.

Average value of the focal length f = …………………. cm



46

Experiment A8: Optics - Determination of Focal Length



47

Experiment A9: Equilibrium of a Suspended Mass


1. newton-spring meter

2. 50 g mass hanger

3. 2 retort stand, boss and clamp

4. 5 slotted mass each 50 g

5. 2 G-clamps

6. protractor

7. thread with three loops



48

1. In this question you will investigate how the force required to maintain equilibrium of a

suspended mass depends on the angle between the line of action of the force and the

horizontal.

You are supplied with a piece of string that has a loop at each end and one in the middle.

(a) (i) Suspend the mass from the middle loop and attach the other loops to a mounted boss anda Newton-meter as shown in Fig. 10.1. The body of the Newton-meter must be clamped so

that it is along the line of action of force F. You may need to rotate the clamp in order to

achieve this. The section AB of the string should be horizontal and the bases of the stands

should be clamped to the bench.



49

(ii) Using the protractor, measure the angle θ. Record the value θ of and the reading F f rom the

newton-meter.

θ = ……..…………..…

F = ………..………….

(iii) Determine the percentage uncertainty in the value of θ.

percentage uncertainty in θ = ……………………..

(b) (i) State two difficulties that you had when making measurements of F and θ.

1…………………………………..………………………………………………………

………………………………………..…………………………………………………

2………………………………………………..…………………………………………

………………………………………………..………………………………………….

(ii) Suggest ways to overcome these difficulties that you mention above.

1…………………………………..………………………………………………………

………………………………………..…………………………………………………

2………………………………………………..…………………………………………

………………………………………………..………………………………………….



50

(c) Change the height of one of the bosses above the bench and adjust the separation of the stands

to give new values of θ and F . The section AB must remain horizontal. You will need to

loosen a G-clamp in order to move a stand. Measure and record the new values of θ and F .

You must ensure that, when you are taking readings, the body of the newton-meter is along

the line of action of the force F and that it does not go off scale.

Include all six sets of values of F , θ and 1/sin θ in your table of results.

(d) Plot a graph of F (y-axis) against

θsin

1(x-axis) and draw the best-fit line through the points

(e) Determine the gradient and y-intercept of the line

Gradient = …………………………………

y-intercept = ………………………………



51



52

(f) The equation that relates F and θ is

F =θsin

mg+ k

where m is the mass of the load, k is constant and g is the acceleration of free fall.

You may take the value of g to be 9.81 ms-2

.

Use your answers from (e) to determine values of m and k . Include appropriate units.

m = ……………………..….

k = …………….…………..



53

Experiment A10: To Make Measurements to Check the Suggested Relationship


1. two half-metre rules

2. two lengths of threads about 60 cm long

3. a metre rule

4. stopwatch (digital)

5. stand and clamp



54

1. A half-metre rule suspended horizontally from 2 parallel threads can be made to oscillate so

that the rule swings horizontally as shown in Fig 11.1 and Fig 11.2. Theory suggests that T,

the period of oscillation, and x, the distance between the supporting threads, are connected by

the relationship:

T = A xb

where A and b are constants.

(a) You are to use the apparatus provided to make measurements to test the suggested

relationship for a support length L of 300 mm as shown in Fig 11.1. Record your

observations.

(b) Also show any necessary calculated values to enable you to test this

relationship.

(c) Draw this graph.

(d) From the graph deduce a value for b.

(e) Comment briefly on the validity or otherwise of the suggested relationship.

Fig. 11.1 Fig. 11.2

plan view

clamp

L

X

support half-metre

rule

support

thread



55

2. Observation.

Validity or otherwise of suggested relationship.

……..………………………………………………………………………………………………

……………..………………………………………………………………………………………

……………………..………………………………………………………………………………

……………………………..………………………………………………………………………



56



57

Experiment A11: To Compare the Temperature of a Water Bath, Measured with a

Mercury in Glass Thermometer (Temperature Measured using a

Thermistor).


1. 3 dry cells

2. switch

3. thermistor rod

4. connecting leads, bare at both ends, of length 50 cm

5. 2 beakers (250 ml) - one with water, the other with ice

6. milliameter - 100 mA

7. termometer

8. bunsen burner

9. wire gauze & tripod stand

10. retort stand and clamp



58

1. In this experiment you will compare the temperature of a water bath, measured with a

mercury-in-glass thermometer, with the temperature as measured using a thermistor.

(a) At the foot of this page, draw a circuit diagram showing the thermistor in series with the

ammeter, the switch, and the source. Connect this circuit, immerse the thermistor and themercury-in-glass thermometer in melting ice, and measure xi, the steady current at t i, the

temperature of the ice.

Record your readings.

(b) Place the thermistor in a water bath and measure x, the current in the circuit, for increasing

values of t , the temperature of the water bath. Readings of x and of t should be taken until

t is between 80oC and 90

oC.

Record your readings.

(c) Plot a graph of t against x, using a temperature scale of 0oC to 100

oC.

Extrapolate your graph so that you may read off xo, x48.5 and x100, the currents P for

values of 0oC, 48.5

oC, and 100

oC respectively.

(d) Calculate the numerical value for θ where θ is given by :

θ =)(

)(100

0100

05.48

x x

x x

2. Circuit



59

3. Results and calculations.



60



61

Experiment A12: Ohm’s Law

Aims

(1) To set up a serial electric circuit to investigate the relationship between

potential difference and current in a resistor and a light bulb.

(2) To determine the resistance of a resistor.(3) To verify if a light bulb obeys Ohm’s law.

(4) To suggest the component(s) inside a given black box.

Apparatus

1. One power supply (0 – 12 V dc)

2. Six connecting wires

3. One digital voltmeter (20 V)

4. One milliammeter (0-10mA) with the smallest div. 0.2mA

5. One ammeter, dual scale (0 – 1 A/5A)

6. One rheostat, 0 – 11 ohm7. One resistor labelled R (use not more than 4 volts on the power supply unit)

8. One light bulb (12 V)

9. One black box labelled X (use not more than 6 volts on the power supply unit)

Reminders:

(i) The circuit should be turned on not more than 20 seconds to avoid overheating.

(ii) use the ammeter, (0 – 5 A) for light bulb.(iii) use the milliammeter (0-10mA) for both R and the black box X, however, test with the ammeter first.

(iv) carry out the experiment with the polarity of power supply reversed as well, for comparison purpose.

Pre-Lab Exercise

1. State Ohm’s law.

………………..…………………..………………..………………..………………..……………

……..…………..……………….…..………………..………………..………………..………[2]

2. Explain why the resistance of a conductor increases with temperature.

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

……..…………..……………….…..………………..………………..………………..………[3]

3. Draw a complete electric circuit to investigate the relationship between potential difference

and current in a resistor.

[3]



62

4. Describe the procedures required to carry out the investigation in part (3).

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

……..…………..……………….…..………………..………………..………………..………[5]

5. State one precaution taken during the measurements.………………..…………………..………………..………………..………………..……………

……..…………..……………….…..………………..………………..………………..………[1]

6. Sketch the symbol for a light bulb.

[1]

Procedure

1. Carry out the procedures that you have designed in the Pre-lab exercise with the apparatus

provided to

(a) determine the resistance of the resistor labelled R.

(b) verify if a light bulb obeys Ohm’s law.

(c) investigate the component(s) inside the black box labelled X.

2. Control of variables in experiment 1(a)

(a) Identify the independent and dependent variables in the experiment.

………………..…………………..………………..………………..………………..…………

……..…………..……………….…..………………..………………..………………..……[2]

(b) State a variable to be kept constant and explain how it is monitored.

………………..…………………..………………..………………..………………..…………

……..…………..……………….…..………………..………………..………………..……[2]



63

3. Tabulation of data for all measurements

Analysis

1. Plot, on the graph papers, the appropriate data for experiments 1(a) and 1(b).

2. State the relationship between the gradient of the graph and the resistance.

..………………..…………………..………………..………………..………………..…………

And hence, determine the resistance of resistor R.

[3]

3. Plot, on another graph paper, the appropriate data for experiment 1(c).

4. Describe the graph obtained for experiment 1(c). Deduce what likely the component(s) in

black box X is (are) to be?

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..…………………..…………..……………….…..………………..………………..………………..………[3]



64



65



66



67

Post-Lab Exercise

1. Explain why the graph for light bulb is not a straight line.

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

……..…………..……………….…..………………..………………..………………..………[3]

2. Discuss why the resistance of a light bulb at a value of p.d. cannot be determined from the

gradient of tangent at that particular p.d.

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

……..…………..……………….…..………………..………………..………………..………[2]

3. By sketching a graph, discuss briefly the variation of p.d across a semiconductor diode with

the current in it.

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

……..…………..……………….…..………………..………………..………………..………[3]



68

Experiment A13: Resistivity

Apparatus requiremens

1. constantan wire, swg 28, of length 1.2m

2. ammeter (0 - 3 A) ± 0.1 A

3. voltmeter (0 - 5 V) ± 0.1 V

4. rheostat, 0 – 11 ohm

5. sliding contact (jockey)

6. power supply (0-12 V dc)

7. switch

8. connecting leads, about 30 cm long, bare at both ends, 3 pieces

9. connecting leads, one end bare and end connected to a crocodile clip, length

about 30 cm, 3 pieces

10. metre rule

11. micrometer screw gauge



69

The resistivity of a conductor of length l metres, cross-sectional area A square metres,

and resistance R ohms is:

l

RAρ

Resistivity is a characteristic of a conductor.

You can determine the resistance of the section of the wire in the circuit diagram below

using:

A

l R

ρ

In this experiment you will calculate the resistivity of a piece of thin wire.

1. Set up the apparatus as shown in the diagram above.

2. Use a micrometer screw gauge to measure the diameter of the nichrome wire five

times. Ask for help if you do not know how to use a micrometer screw gauge.Assume the wire has a uniform cross-section.

3. Calculate the mean diameter of the nichrome wire.

4. Calculate the cross-sectional area of the nichrome wire.

5. Set the power supply to 6V and switch on your circuit.

6. Move the sliding contact so the current flows through 1.00 m of the nichrome wire.

Record the potential difference across l, and the current flowing in the circuit.

7. Repeat step 6 for lengths of nichrome of 0.80, 0.60, 0.40 and 0.20 m.

rheostat

A

V

l

power supply

metre rule

sliding contact

constantan wire



70

8. Tabulate all your readings.

9. Plot the resistance R against length l to determine the gradient of the resulting graph.

10. Determine the resistivity of the wire.

11. What can you say about the relationship between the resistance R of a wire and its

length l?

………………..…………………..………………..………………..………………..……………

………………..…………………..………………..………………..………………..……………

Tabulation

Calculation



71



72

Experiment A14:

Aims

(i) To determine the e.m.f. and the Internal Resistance of a Dry Cell

(ii) determine the Value of External Resistance when the Power Output is a Maximum.


1 battery of 2 dry cells

2 cell holder

3 ammeter 0 – 1 A ± 0.1 A

4 voltmeter 0 – 3 V ± 0.1 V

5 six 2.0 Ω resistors soldered in series, each of power rating ½ W

6 a fixed 5 Ω resistor, ½ watt

7 connecting leads, bare at both ends, of length about 30 cm, 3 pieces

8 connecting leads, one end bare and the other end connected to a crocodile clip, 2

pieces



73

A

V

dry cell or

potato cell

R

E r

(i) In this experiment you will use a graphical method to determine the e.m.f. and the internal

resistance of a battery.

Theory

The circuit diagram below shows a circuit of a battery connected in series with an ammeter and avariable resistor R. The high resistance voltmeter is connected across the variable resistor to

measure the potential difference V across it.

Applying Kirchhoff’s second law,

E = V R + V rSince V r = Ir , hence E = V R + Ir

Rearranging, V R = - rI + E

If a graph of V R against I is plotted, the gradient of the graph = -r and the y-intercept of the graph

= E.



74

fixed resistor

2.0

A

V

2.0 2.0 2.0 2.0 2.0

Dry cells

The circuit diagram for the experiment is shown below.

The fixed resistor in series with the battery is to simulate a larger internal resistance than is

actually present.

The set of the six 2.0 resistors in series act as the variable resistors.


1 Connect the circuit up as shown in the diagram. With the crocodile clip connected to the

position shown, measure the potential difference V across the 2.0 resistor and the current I

passing through it. Repeat your measurements and calculate the average values for your V and I.

2 Repeat 1 for different values of R until you have 6 sets of reading for V and I .



75


1 (i) Record all your sets of results for R, V and I in a table of results. .

Analysing your data

1 Determine the gradient and the y-intercept of your graph.



76

2 The internal resistance r of the battery (including the resistance of the fixed resistor) is

given by the equation

r = - gradient

The e.m.f. E of the cell is given by the equation

E = y-intercept

Use your answer to 1 to determine the internal resistance and the e.m.f. of the battery.

The internal resistance of the battery calculated above includes the resistance of the fixed resistor

of resistance 5.0 . What is the actual internal resistance of the battery?



77



78

(ii) In this experiment you will use a graphical method to determine the value of the external

resistance R at which the output power of a dry cell is a maximum.

Copy the table in experiment (i) above. Add an additional column to your table for the output

power P dissipated in the external resistors of the circuit using the following formula

P = VI

Tabulation

Analysing your data

Plot a graph of power output P against the external resistance R.

Determine the value of R at which the power output P is a maximum.

Your may consider the 5.0 resistor as part of the internal resistance of the cell.

Comment on the relationship between the maximum output power P, the external resistance R and

the internal resistance r of the source.

………….……………………………………………………………………………………………

…………………………………………………………………………………………….................



79



80

Experiment 15: Potential Divider

Aims

(1) To set up a serial electric circuit to investigate how a potential divider operates.

(2) To investigate how the brightness (Power) of a light bulb affects the output p.d. across a light

dependent resistor (LDR).

Apparatus

Common items

1. Battery of two dry cells (1.5 V each)2. One cell holder

3. Ten connecting leads

4. One digital voltmeter (20V)

5. One analogue voltmeter 5V

Experiment 11. One fixed 5 k Ω resistor (R1)

2. Five 1 k Ω resistors soldered in series (R2)

Experiment 2

1. One ammeter (dual scale 1A/5A)

2. A power supply unit (d.c.)

3. A light bulb 12V4. A light dependent resistor (LDR) in series with a 10 k Ω resistor.

5. A short hollow tube

Reminder:

The circuit should be turned on not more than 20 seconds to avoid overheating.

Pre-Lab Exercise

1. State Kirchhoff’s 2nd law.

………………..………………..…………….…..………………..………………..……………

..…………..….………….…..………………..………………..………………..……………[1]

2. State which electrical quantity is the same in two resistors connected in series

……………..….………….…..………………..………………..………………..……………[1]



81

3. The electric circuit to investigate how a potential divider operates is shown below. R1 is the

fixed 5 k Ω resistor while R2 is the combination of 1 k Ω resistors in series.

(a) State the formula for the p.d. across R2 (V2) in terms of I and R2.

………………..….………….…..………………..………………..………………..………[1]

(b) State the formula for the total p.d. across R1 and R2 (VT) in terms of I, R1 and R2.

...…………..…………………..………………..………………..………………..……...[1]

(c) Use your answers to part (a) and (b) to deduce the formula for V2 in terms or R1, R2 and

VT

[1]

4. For experiment 1, describe the procedures required to investigate how the p.d. across R2

varies with the values of R2.

……………..…………………..………………...………………..……………….……………..

……………..…………………..………………..……………..………………..………………..

……………..…………………..………………...………………..……………….……………..

……………..…………………..………………..……………..………………..………………..

……………..…………………..………………..……………..………………..………………..

……………..……………….…..………………..……………..………………..……………[2]

V2

R1

R2

V1



82

5. For experiment 2, describe the procedures required to investigate how the power of a light

bulb affects the output p.d. across a LDR.

You should explain how the power of a bulb is determined and how the external light from the

surroundings can be avoided from reaching the LDR.

……………..…………………..………………...………………..……………….……………..

……………..…………………..………………...………………..……………….……………..

……………..…………………..………………..……………..………………..………………..

……………..…………………..………………...………………..……………….……………..

……………..…………………..………………..……………..………………..………………..

……………..…………………..………………...………………..……………….……………..

……………..…………………..………………..……………..………………..………………..

……………..…………………..………………..……………..………………..………………..

……………..……………….…..………………..……………..………………..……………[4]

6. Why must a fixed resistor be connected in series with the LDR?

……………..…………………..………………..……………..………………..………………..

……………..…………………..………………..……………..………………..………………..

……………..……………….…..………………..……………..………………..……………[2]

7. For experiment 2,

(a) What is the independent variable?

………..…………………..………………..………………..…………..………………….[1]

(b) What is the dependent variable?

………..…………………..………………..………………..…………..………………….[1]

(c) What are the variables which should be kept constant throughout the experiment?

....……..…………………..………………..………………..…………..………………….[1]

………..…………………..………………..………………..…………..………………….[1]



83

Experiment 1:

Procedure

Carry out the procedures that you have designed in the Pre-lab exercise with the apparatus

provided to determine how the p.d. across R2 varies with the values of R2.

Tabulation of data.Include in your table values of R2,V2 and VT.

Analysis

1. Using the formula in 3 (c) above, calculate, for all the values of R2, the corresponding values

of V2 . Record your answers in the table above.

2. Compare and comment on the measured and the calculated values of V2 .

………………..……………..…..……………….……………..………………..………………

.………………..……………..…..……………..….….………..………………..………………

.....………………..……………….…..…………...….…………..………………..…………[2]

3. If R1 and R2 were replaced with the two 2 Ω resistors, calculate the value of V2.

V2 = ………………………. [1]



84

Experiment 2:

Procedure

Carry out the procedures that you have designed in the Pre-lab exercise with the apparatus

provided to investigate how the power P of a light bulb affects the output p.d. V across a LDR.

Tabulation of data.

Analysis

1. Plot a suitable graph to investigate the relationship between power P of a light bulb and the

output p.d. V across a LDR.

………………..……………..…..……………….……………..………………..………………

.………………..……………..…..……………..….….………..………………..………………

....………………..……………….…..…………...….…………..………………..…………[2]



85



86

Post-lab exercise

1. Explain why the resistance of the LDR changes with the brightness of light bulb.

………………..……………..…..……………….……………..………………..………………

.………………..……………..…..……………..….….………..………………..………………

....………………..……………….…..…………...….…………..………………..…………[2]

2. Explain how the output p.d. across the LDR changes with its resistance.

………………..……………..…..……………….……………..………………..………………

.………………..……………..…..……………..….….………..………………..………………

....………………..……………….…..…………...….…………..………………..…………[2]

3. A light dependent resistance (LDR) is connected in series with a fixed resistor R as shown in

the diagram below. A p.d. of 5 V is applied across XY.

The resistance of is 20 k when it is in the dark but drops to 0.4 k in bright light.What is the corresponding change in the potential at point Y?

change in the potential = ……………………….V

+5 V

Z

0 V

R = 500

X

Y



87

Experiment A16: To Determine the Resistance of a Voltmeter by a Simple Graphical

Method


1. analogue voltmeter, 0 – 5 V

2. power pack (2 V d.c.)

3. resistors of values about 5 kΩ, 6 kΩ, 7 kΩ, 8 kΩ, 9 kΩ and 10 kΩ soldered in

series.

4. connecting leads, bare at both ends, 1 length

5. connecting leads, one end bare and the other connected to a crocodile clip, 2

lengths



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Theory

1. Let E represent the total e.m.f. of the circuit, R the resistance reading, V the voltmeter reading

and Rv the voltmeter.

2. Then the current Ι in the circuit isV R R

E I

assuming the resistance of the power supply

in the circuit is negligible.

3. Hence, the voltage across the voltmeter is V V V R R R E IRV

4. Rearranging,

V

ER R R V V

1

V

V

RV

ER

R

5. Thus, the graph of R againstV

1is a straight line whose negative intercept

on the R axis is the magnitude RV.

Making measurement and observation

1. Connect up the circuit as shown in Fig 17.

2. Select the resistor of the smallest value. You may get the values of the resistors from the

colour codes on the resistors. Alternatively you may measure the resistance of the resistors using

a ohmmeter. Record the resistance R and the voltmeter reading V .

3. Repeat by increasing R in steps of 10 k Ω.

V R

FIG. 17



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4. Tabulation.

5. Plot a graph with values of R as ordinates against the corresponding values of V

1as abcissae.

6. Determine the resistance RV of the voltmeter. Record your answer to 3 s.f.



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Experiment A17: Compound Pendulum


1. stiff wire (s.w.g 18)

2. plasticine (13g)

3. stopwatch

4. 1 pair of wooden blocks (5 cm x 4 cm)

5. stand and clamp

6. half-metre rule

7. stout pin



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x

pin or nail

stiff wire

plasticine

1. A pendulum can be formed from a length of stiff wire and a bob of plasticine moulded into a

spherical shape (Fig. 18.1). If the pendulum is made to oscillate in a plane containing itself and

its supporting pin, T, the period of small oscillations will depend on where the plasticine bob is

placed on the wire.

(a) Your apparatus includes a piece of stiff wire which has a loop at one end. Use this,together with other apparatus, to make pendulum as shown in Fig 18.1. This will be used

to investigate the effect on T of changing the position of the bob.

(b) Displace the pendulum so that it swings with small oscillations in the plane containing the

support pin. Make measurements to determine T for different values of x, the distance of

the center of gravity of the bob from the point of support. This distance is shown in Fig.

18.2. Record your observations. The distance x should be varied between about 20 mm

and 110 mm.

Fig. 18.1 Fig. 18.2



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Observations.

(c) Draw a graph of T against x.

(d) From the graph deduce the value of x when T is a minimum.

Record this value.



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Experiment A18: Nov 2009 Paper 31 Q1


1. Round wooden rod between 20 mm and 25 mm in diameter and 20 cm in length (e.g. a section of broom handle). Ends should be cut squarely.

2 Screw hook.

3 50 g laboratory mass.

4 Five expendable springs (Philip Harris catalogue number B8A41397).

5 Tall 1 litre transparent beaker (or similar transparent container about 20 cm tall and 8 cm diameter).

6 Beaker (or similar container) containing about 1 litre of water.

7 Tall retort stand (at least 0.7 m high). Boss and clamp.

8 Half-metre rule, with a millimetre scale.

9 Stopwatch reading to 0.1 s or better.

10 Vernier calipers (these can be shared between two or three candidates).

11 Paper towels.



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Nov 2009 Paper 31 Q1

You may not need to use all of the materials provided.

1 In this experiment you will investigate the position of a wooden rod suspended in water as the

depth of the water is varied.

Assemble the apparatus, as shown in Fig. 1.1, then add water to the beaker until the mass

attached to the bottom of the rod is completely covered and is not touching the bottom of the

beaker.

(a) Record h and z, as shown in Fig. 1.1.

h = ………………………………… cm

z = ………………………………… cm

(b) Add more water to the beaker and repeat (a). Repeat this procedure until you have six sets of

readings for h and z.



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(c) (i) Plot a graph of z on the y-axis against h on the x-axis. Draw the line of best fit.

(ii) Determine the gradient of the line.

gradient = …………………………………



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(d) (i) Use the vernier calipers to determine the diameter d of the wooden part of the rod.

d = …………………………………

(ii) Calculate the cross-sectional area A of the wooden part of the rod, using the relationship

A =4

2d π

A = ………………………………… m2

(e) The relationship between z and h is

z = c + h

1

Ag

k

ρ

where c is a constant, k is the spring constant, ρ is the density of water (1000 kg m-3

), and g is the

acceleration of free fall (9.81 m s-2

).

Using your answers from (c)(ii) and (d)(ii), determine the value of k. Give an appropriate unit.

As Physics Practical Set 1 Updated April 2014

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Transcript of As Physics Practical Set 1 Updated April 2014