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Cambridge IGCSE™
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PHYSICS 0625/42
Paper 4 Theory (Extended) February/March 2025

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 9.8 N (acceleration of free fall = 9.8 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. Any blank pages are indicated.

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2

1 Fig. 1.1 shows a force–extension graph for a spring.

5000

4000
force / N

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3000

2000

1000

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–0.04 –0.02 0.02 0.04 0.06 0.08 0.10
extension / m

Fig. 1.1

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(a) Calculate the spring constant k of the spring.

k = ......................................................... [2]

(b) A student states that the spring has not reached the limit of proportionality when a force of
4500 N is applied to it.
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State how the graph shows that this statement is true.

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

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

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(c) Springs can be compressed by forces. The spring described by Fig. 1.1 is compressed by a
force F and has an extension of –0.025 m.

Determine F.
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F = ......................................................... [2]

(d) State whether force is a scalar quantity or a vector quantity. Explain your answer.

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

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

[Total: 6]
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4

2 Trolley A and trolley B are on a horizontal, frictionless bench. Trolley A moves to the right with a
constant velocity u = 0.44 m / s. Trolley B is stationary.

Fig. 2.1 shows trolley A before it collides with trolley B.

direction of motion

A B

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bench

Fig. 2.1 (not drawn to scale)

(a) State the momentum of trolley B before the collision. Explain your answer.

statement ..................................................................................................................................

explanation ...............................................................................................................................

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

(b) After the collision, the two trolleys are joined together and travel with a constant velocity
v = 0.18 m / s to the right. The mass of trolley A is 0.75 kg.

Calculate the mass of trolley B.

mass of trolley B = ......................................................... [3] DO NOT WRITE IN THIS MARGIN

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(c) (i) The trolleys move onto a rough surface which exerts a constant force F on the trolleys
and brings them to rest in 2.6 s.

Calculate F.
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F = ......................................................... [2]

(ii) A different rough surface exerts a smaller resistive force on the trolleys. State how this
affects the time taken to bring the trolleys to rest. Explain your answer.

statement ..........................................................................................................................

explanation ........................................................................................................................

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

[Total: 7]
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6

3 Fig. 3.1 shows a mains electric heater used to heat a small room.

shiny metal surface

heating elements

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Fig. 3.1

(a) State the region of the electromagnetic spectrum which radiates thermal energy from the
heater.

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

(b) Explain why the shiny metal surface behind the heating elements increases the thermal
energy radiated into the room.

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

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

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

(c) The metal outer casing of the heater is earthed. State why this is an important safety feature.

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

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

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(d) The mains voltage is 230 V. The two identical heating elements are connected in parallel.
Each heating element has a resistance of 89 Ω.

(i) Calculate the current in one heating element.

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current = ......................................................... [2]

(ii) Show that the electrical power of the heater is approximately 1200 W. State any equation
you use in words or symbols.
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[2]

(iii) The heater is 95% efficient at converting electrical work done to thermal energy.

Calculate the thermal energy emitted by the heater in (d)(ii) in 60 s. Give your answer to
two significant figures.
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thermal energy = ......................................................... [3]

[Total: 11]
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8

4 A train has a maximum speed of 200 km / h. It accelerates from rest with constant acceleration of
0.70 m / s2.

(a) (i) Define acceleration.

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

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

(ii) Show that the maximum speed of the train is approximately 56 m / s.

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[2]

(iii) Calculate the time taken for the train to reach its maximum speed.

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time = ......................................................... [2]

(b) (i) The train has a total mass of 440 000 kg. Calculate the force which causes the
acceleration of the train.

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force = ......................................................... [2]

(ii) The train travels into a headwind. The force of this headwind opposes the motion of the
train. State and explain the effect of this force on the motion of the train.

statement ..........................................................................................................................

explanation ........................................................................................................................

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

[Total: 8]

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5 A light-dependent resistor (LDR) has a low resistance in high light intensity and a high resistance
in the dark.

(a) Sketch a graph of resistance (y-axis) against light intensity (x-axis) for an LDR.
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[2]

(b) Fig. 5.1 shows part of the electric circuit used to turn on a light when it is dark.

fixed resistor
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Fig. 5.1
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(i) Complete the circuit in Fig. 5.1 with the symbol for a light-dependent resistor (LDR). [1]

(ii) Explain why the lamp is off in the light and the lamp is on in the dark. Use ideas about
potential difference (p.d.) in your answer.

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

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

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

..................................................................................................................................... [3]
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[Total: 6]

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6 Fig. 6.1 shows an object O which is 5.0 cm away from the centre of a thin, converging lens L. The
focal length of L is 3.0 cm. Fig. 6.1 is drawn to full scale.

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O

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Fig. 6.1

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(a) (i) On Fig. 6.1, label the principal axis with a P. [1]

(ii) On Fig. 6.1, place a letter X at a focal point. [1]

(iii) On Fig. 6.1, draw two rays from O to locate the tip of the image produced by the lens. [2] DO NOT WRITE IN THIS MARGIN

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(iv) In Table 6.1, place a tick in the right-hand column next to all the terms that describe the
image in (a)(iii).

Table 6.1

diminished

enlarged

inverted
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real

same size

upright

virtual
[3]

(b) The object moves closer to L. The new distance between L and the object is less than the
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focal length of L.

Describe how the new image is different from the image in (a)(iv).

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

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

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

[Total: 9]
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7 (a) Fig. 7.1 is a scale drawing of light waves approaching a narrow slit.

SCALE 1.0 cm : 4.0 × 10–7m

direction of

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propagation
of light

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crests of
3 successive barrier with
wavefronts narrow slit

Fig. 7.1

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(i) Name the wave effect produced by the narrow slit.

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

(ii) Using Fig. 7.1, determine the wavelength of the light. Give your answer to two significant
figures.
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wavelength = ......................................................... [2]

(iii) On Fig. 7.1, draw three wavefronts that have passed through the narrow slit. [3]

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(b) A foghorn emits a sound with frequency 380 Hz. The sound is heard by a ship 2.5 km away
from the foghorn. The speed of sound in air is 330 m / s.

(i) Show that the wavelength of the sound is approximately 0.9 m.

State any equation you use in words or symbols.
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[2]

(ii) Calculate the time it takes for sound to travel to the ship from the foghorn.
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time = ......................................................... [2]

[Total: 10]
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8 Fig. 8.1 shows a metal rod suspended in the magnetic field produced by a pair of permanent
magnets. The metal rod is connected to a cell and there is a current in the metal rod.

N S

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metal rod

Fig. 8.1

(a) State the direction of the force on the metal rod due to the current.

Explain your answer.

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

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explanation ...............................................................................................................................

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

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

(b) The connections to the cell are reversed.

State how this change affects the force on the metal rod.

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

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(c) Two magnets and a cell are used to make a simple electric motor as shown in Fig. 8.2.

L magnets

N S
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K
J M

cell

Fig. 8.2

Describe the function of parts J, K, L and M.

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J ................................................................................................................................................

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

K ...............................................................................................................................................

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

L ................................................................................................................................................

...................................................................................................................................................
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M ...............................................................................................................................................

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

[Total: 8]
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16

9 Strontium-90 is a radioactive isotope of strontium. The nuclide notation for strontium-90 is:

9 0 Sr
38

(a) (i) Explain what isotopes are.

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

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

(ii) Complete Table 9.1 for strontium-90.

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Table 9.1

particle number in one atom location

38 outside nucleus

neutron

38 inside nucleus

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[2]

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(b) Strontium-90 is used to measure the thickness of metal sheets in industry.

Strontium-90 decays by emitting beta (β) particles which pass through a metal sheet to a
detector.

(i) One metal sheet is 0.75 mm thick. Suggest why strontium-90 is a suitable radioactive
source to measure the thickness of the metal sheets.

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

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

(ii) The half-life of strontium-90 is approximately 27 years. Fig. 9.1 shows the shape of a
decay curve.

100

percentage of
75
strontium-90
remaining
50
0

25
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0
0 5 10 15 20 25 30 35 40 45 50 55 60
age of sample / years

Fig. 9.1

The strontium-90 source is replaced with a new source after 15 years. Using Fig. 9.1,
suggest why a strontium-90 source that is more than 15 years old needs to be replaced
with a new source.

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

[Total: 7]
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10 Fig. 10.1 shows the path of the Earth as it orbits the Sun. X is a position on the Earth where
scientists observe the apparent motion of the Sun throughout the year.

North Pole
E
X

Equator
Earth’s orbit

F H

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X X
Sun

G X

Fig. 10.1

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(a) Determine how many days it takes the Earth to move around its orbit from F to G.
Explain your answer.

number of days = ..............................

explanation ...............................................................................................................................

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

(b) Fig. 10.1 shows four positions E, F, G and H of the Earth in its orbit of the Sun.

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(i) Identify the position of the Earth when it is summer at X. .............................. [1]

(ii) Identify the position of the Earth when it is winter at X. .............................. [1]
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(c) The orbital speed of the Earth around the Sun is approximately 3.0 × 104 m / s.

Calculate the average radius of the Earth’s orbit.

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radius = ......................................................... [3]

(d) Earth is a planet in the Solar System. State one other type of naturally occurring object that
is present in the Solar System.

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

[Total: 8]
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