Cambridge IGCSE™

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PHYSICS 0625/31
Paper 3 Theory (Core) October/November 2020

1 hour 15 minutes

You must answer on the question paper.

No additional materials are needed.

INSTRUCTIONS
● Answer all questions.
● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs.
● Write your name, centre number and candidate number in the boxes at the top of the page.
● Write your answer to each question in the space provided.
● Do not use an erasable pen or correction fluid.
● Do not write on any bar codes.
● You may use a calculator.
● You should show all your working and use appropriate units.
● Take the weight of 1.0 kg to be 10 N (acceleration of free fall = 10 m / s2).

INFORMATION
● The total mark for this paper is 80.
● The number of marks for each question or part question is shown in brackets [ ].

This document has 20 pages. Blank pages are indicated.

DC (CE/CGW) 196073/5
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1 Student P and student Q run in a 100 m race.

Fig. 1.1 shows the distance–time graph for each student during the race.

100

distance / m

80

60

40

20

0
0 2.0 4.0 6.0 8.0 10.0 12.0
time / s
Key

student P
student Q

Fig. 1.1

(a) Determine the time taken for student Q to run 100 m.

time = ...................................................... s [1]

(b) Determine the distance between the two students as Q reaches 100 m.

distance = ..................................................... m [1]

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(c) Calculate the average speed of student Q during the 100 m race.

average speed = ................................................. m / s [3]

(d) State which student has the faster speed between 3.0 s and 6.0 s.

Explain how Fig. 1.1 allows you to compare speeds without calculation.

...................................................................................................................................................

...................................................................................................................................................

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

[Total: 6]

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2 Fig. 2.1 shows a beaker containing liquid on a top pan balance.

liquid

Fig. 2.1

The mass of the empty beaker is 400 g.

(a) Using the information in Fig. 2.1, determine the mass of the liquid in the beaker.

mass = ...................................................... g [1]

(b) The beaker contains 750 cm3 of liquid.

Calculate the density of the liquid.

density = .............................................. g / cm3 [3]

(c) Calculate the weight of the empty beaker.

weight = ..................................................... N [4]

[Total: 8]

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3 Fig. 3.1 shows three horizontal forces acting on a car as it moves along a straight road.

The horizontal forces act along the same straight line.

250 N
900 N
300 N

Fig. 3.1

(a) (i) Calculate the size of the resultant horizontal force on the car and state its direction.

size of resultant force = ........................................................... N

direction of resultant force ...............................................................

[3]

(ii) The driver presses the brake pedal and the car slows down.
As the car slows down, the kinetic energy of the car decreases by 100 kJ.

Describe and explain what happens to this 100 kJ of energy.

...........................................................................................................................................

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

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(b) Fig. 3.2 shows the force applied to the brake pedal by the driver’s foot.

pivot 20 cm
35 N

brake pedal

Fig. 3.2

Calculate the moment of the force about the pivot. Include the unit.

moment = ..................................... unit ................ [4]

[Total: 9]

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4 Electrical energy is provided to homes and industry from a coal-fired power station.

(a) The main stages in the operation of a coal-fired power station are listed below.

They are not in the correct order.

A The boiler produces steam.

B The turbine turns a generator.
C Thermal energy transfers to water in a boiler.
D Chemical energy in coal transfers to thermal energy.
E The generator produces electrical energy.
F Steam turns a turbine.
G Coal burns in a furnace.

Complete the flow chart to describe how a coal-fired power station works.

Insert the missing letters in the empty boxes.

[3]

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(b) Some people are against the use of coal-fired power stations.

Give two environmental problems caused by coal-fired power stations.

1. ...............................................................................................................................................

...................................................................................................................................................

2. ...............................................................................................................................................

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

(c) In the power station, a conveyor belt lifts coal from a coal supply to a furnace. An electric
motor moves the conveyor belt. Fig. 4.1 shows this arrangement.

coal supply
conveyor belt

coal

input to furnace

Fig. 4.1

The speed of the electric motor increases and the coal supply rate is increased. The conveyor
belt lifts more coal each second. State the effect, if any, of increasing the motor speed on:

(i) the work done on each kilogram of coal

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

(ii) the output power of the motor.

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

[Total: 7]

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5 Fig. 5.1 shows a steel container fitted with a liquid manometer. There is a gas in the container.

sealed lid
liquid
manometer
steel container

100 mm
gas

bench mercury

Fig. 5.1

(a) (i) The area of the steel container in contact with the bench is 80 cm2. The total weight of
the steel container and its contents is 60 N.

Calculate the pressure that the steel container exerts on the bench.

pressure on the bench = ............................................. N / cm2 [3]

(ii) Atmospheric pressure is equal to 760 mm of mercury (mm Hg).

Determine the pressure inside the container in mm Hg.

pressure = ............................................. mm Hg [2]

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(b) The temperature of the gas inside the steel container decreases.

State and explain how the pressure of the gas changes as the temperature of the gas
decreases.

Use your ideas about molecules in your answer.

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

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

[Total: 8]

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6 (a) Fig. 6.1 represents three changes of state. Each pair of diagrams A, B and C shows the
arrangement of molecules in a substance before and after it changes state.

before after

Fig. 6.1

Give the term used for each change of state.

A ...........................................................

B ...........................................................

C ...........................................................
[3]

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(b) A student attaches a liquid-in-glass thermometer to a ruler. The thermometer does not have a
marked scale. Fig. 6.2 shows the arrangement.

cm ruler
15
14 thermometer
13
12
11
10
9
8
7 mercury level
6
5
4
3
2
1
0

Fig. 6.2

The student places the thermometer in steam. The mercury rises to 11 cm on the ruler.

The student places the thermometer in melting ice. The mercury decreases to 1 cm on the
ruler.

Determine the temperature indicated by the mercury level in Fig. 6.2.

temperature = .................................................... °C [3]

[Total: 6]

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7 (a) Fig. 7.1 shows a ray of light incident on a plane mirror at point X.

plane mirror
X
40°

ray of
light

Fig. 7.1 (not to scale)

(i) Determine the value of the angle of reflection for the ray of light at point X.

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

(ii) On Fig. 7.1:

• draw the normal at point X and label the normal with the letter N
• draw the ray reflected from point X.
[2]

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(b) Fig. 7.2 shows how a converging lens forms an image of an object.

28 cm 12 cm 9.0 cm

object

image

Fig. 7.2 (not to scale)

(i) Determine the focal length of the lens.

focal length = ................................................... cm [1]

(ii) Determine the distance of the image from the lens.

distance = ................................................... cm [1]

(iii) Describe the nature of the image formed by the lens in Fig. 7.2.

...........................................................................................................................................

...........................................................................................................................................

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

[Total: 7]

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8 Fig. 8.1 shows a mobile (cell) phone.

Fig. 8.1

(a) (i) State the type of electromagnetic wave used for the mobile phone signal.

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

(ii) The screen of the mobile phone emits visible light. State one type of electromagnetic
wave with a shorter wavelength than visible light.

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

(b) The mobile phone produces sound waves.

(i) State the range of audible frequencies for a healthy human ear. Include the unit.

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

(ii) The ring tone of the mobile phone consists of two musical notes, note A and note B.

Note A is louder and is higher in pitch than note B.

Fig. 8.2 shows note A displayed on an oscilloscope screen.

Fig. 8.2

Note B is displayed on the same oscilloscope screen as note A. Describe the differences
between the wave for note B and the wave for note A. You may draw on Fig. 8.2 to show
the differences.

...........................................................................................................................................

..................................................................................................................................... [2]
[Total: 6]

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9 A student has a permanent bar magnet and two metal bars, as shown in Fig. 9.1.

P R

permanent bar
S N
magnet

Q S

metal bar PQ metal bar RS

Fig. 9.1

The student tests bar PQ and bar RS separately. He holds the N pole of the permanent bar magnet
close to each end of each metal bar. Table 9.1 shows the results of the tests.

Table 9.1

end of metal bar result of test with

N pole
P attracted
Q repelled
R attracted
S attracted

Deduce whether each metal bar is a magnet, an unmagnetised magnetic material or a

non-magnetic material.

Give a reason for each of your answers.

1. metal bar PQ ............................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

2. metal bar RS .............................................................................................................................

...................................................................................................................................................

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

[Total: 4]

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10 A student determines the resistance of a piece of metal wire XY.

Fig. 10.1 shows the wire connected in the circuit.

variable A
resistor

X Y

wire

Fig. 10.1

(a) (i) The student measures the potential difference (p.d.) across the wire XY.
On Fig. 10.1, show the voltmeter correctly connected. Use the correct symbol. [1]

(ii) There is a current in the wire. State the name of the particles that flow through the wire.

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

(iii) The student removes wire XY and replaces it with another wire CD. Wire CD is the same
length and is made of the same material as wire XY, but thinner.

State any difference between the current in wire CD and the current in wire XY. Explain
your answer.

...........................................................................................................................................

...........................................................................................................................................

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

(iv) State the unit used for the electromotive force (e.m.f.) of the battery.

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

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(b) (i) The resistance of wire CD is 8.7 Ω and the resistance of the variable resistor is 7.4 Ω.

Determine the combined resistance of the wire CD and the variable resistor.

resistance = ..................................................... Ω  [1]

(ii) The current in the variable resistor is 0.40 A.

State the current in wire CD.

current = ...................................................... A [1]

[Total: 7]

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11 (a) Fig. 11.1 represents the particles in a neutral lithium atom.

orbits

Fig. 11.1

Use the information in Fig. 11.1 about the lithium atom to answer (a)(i), (a)(ii) and (a)(iii).

(i) Determine the number of electrons. ...................................................... [1]

(ii) Determine the value of the nucleon number. ........................................ [1]

(iii) Determine the number of neutrons. ...................................................... [1]

(b) The count rate of a radioactive sample is 2400 counts per minute at 10 am on one day. The
half-life of the sample is two days.

Predict the count rate at 10 am four days later.

count rate = ........................... counts per minute [3]

[Total: 6]

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12 (a) Fig. 12.1 shows two circuits, A and B, linked by a relay.

relay
heater
switch S

relay
+ switch R
6V
-
relay coil

120 V a.c.

circuit A circuit B

Fig. 12.1

Describe what happens in the two circuits when switch S is closed.

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

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

(b) Another circuit includes a transformer. The input voltage of the transformer is 120 V a.c.
The input coil has 480 turns of wire and the output coil has 60 turns of wire.

Calculate the output voltage of the transformer.

output voltage = ...................................................... V [3]

[Total: 6]

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