IGCSE Physics 0625/21 May/June 2025 Past Paper with Answers

Question 1

On a speed-time graph, which feature shows that the acceleration of an object is changing?

1. a curved line
2. a straight sloping line
3. a horizontal line
4. a line through the origin

Question 2

An aircraft has a lift of 120 kN upward, a weight of 60 kN downward, a thrust of 60 kN forward and a drag of 40 kN backward. What is the magnitude of the resultant force?

1. about 63 kN
2. about 40 kN
3. 280 kN
4. 0 kN

Question 3

Two metal blocks have exactly the same dimensions but, when each hangs from an identical force meter, the meters show different readings. Which statement is correct?

1. Equal volumes and different weights
2. Different volumes and equal weights
3. Equal volumes and equal weights
4. Different volumes and different weights

Question 4 · Answer A

Density = mass divided by volume. A balance measures the mass of the necklace. Its volume, since the shape is irregular, is found from the rise in water level in a measuring cylinder. No thermometer or stopwatch is needed.

Question 5 · Answer A

The spring constant = change in force divided by change in extension. The extra load is 8.0 - 3.0 = 5.0 N. The extra extension is 30 - 20 = 10 cm. So the spring constant = 5.0 / 10 = 0.50 N/cm.

Question 6 · Answer A

A block is in equilibrium when the resultant force on it is zero. Two equal forces acting in opposite directions cancel out, giving zero resultant force, so the block is in equilibrium.

Question 7 · Answer A

Force equals the change of momentum divided by the time taken, not multiplied by time, so the statement in "Force equals change of momentum multiplied by time" is the incorrect one. Impulse does equal change of momentum, momentum is mass multiplied by velocity, and momentum is conserved in a closed system, so those statements are all correct.

Question 8 · Answer A

From F = ma, the acceleration a = F divided by m. With the force F kept constant, reducing the mass m increases the acceleration. Temperature, the ball being hollow, and the density do not affect the acceleration if the mass and force are unchanged.

Question 9 · Answer A

Pressure = force divided by area. The weight (force) is the same for both carts. Wide wheels have a larger contact area with the ground, so they exert a lower pressure. Lower pressure means the wheels sink less into soft ground.

Question 10 · Answer A

In a gas the particles are much farther apart than in a liquid, so the separation is greater. A hot gas also has more thermal energy than a cool liquid, so its particles move faster on average. Hence greater separation and faster motion.

Question 11 · Answer A

At constant temperature, pressure multiplied by volume is constant: p1 V1 = p2 V2. So 300 x 2.0 = p2 x 5.0, giving 600 = 5.0 p2, so p2 = 600 / 5.0 = 120 kPa.

Question 12 · Answer A

Specific heat capacity is the energy needed to raise the temperature of 1 kg of a substance by 1 degree C. A greater specific heat capacity for P means more energy is needed to raise 1 kg of P by 1 degree C than for the same mass of Q. Specific heat capacity is about temperature change, not melting.

Question 13 · Answer A

Water is made of molecules. During evaporation, the most energetic individual water molecules at the surface escape into the air. They leave one at a time as separate molecules, not as atoms, protons or droplets.

Question 14 · Answer A

Heating the gas gives the particles more kinetic energy, so they move faster. Faster particles hit the container walls harder and more frequently. More frequent and harder collisions per unit area mean a greater force per unit area, which is a higher pressure.

Question 15 · Answer A

Copper is a much better thermal conductor than wood. The copper rod conducts thermal energy away from the warm hand quickly towards the cold ice, so the hand loses heat fast and the rod feels colder. Wood is a poor conductor, so little heat flows and it feels less cold.

Question 16 · Answer A

A dull black surface is the best absorber of infrared radiation and also the best emitter. So compared with a white surface at the same temperature, the black surface has both a higher rate of absorption and a higher rate of emission. Good absorbers are always good emitters.

Question 17 · Answer A

In a transverse wave the particles vibrate at right angles to the direction the wave travels. The wave moves horizontally, so the water surface and the floating cork move up and down about a fixed point. The cork is not carried along with the wave.

Question 18 · Answer A

When the object is inside the focal length of a converging lens, the lens acts as a magnifying glass. The image formed is virtual, upright and enlarged, and it is on the same side of the lens as the object.

Question 19 · Answer A

When a ray reflects from two mirrors that are at 90 degrees to each other, the law of reflection applied twice turns the ray through a total of 180 degrees. The emerging ray is therefore parallel to the incident ray but travelling in the opposite direction. This is the principle of a corner reflector.

Question 20 · Answer A

Refractive index n = speed of light in air divided by speed of light in the material. If the speed in the material is one half of the speed in air, then n = 1 divided by 0.5 = 2.0.

Question 21 · Answer A

Dispersion is the separation of white light into its component colours. It happens because each colour has a slightly different speed in glass and so is refracted by a different amount, spreading the colours into a spectrum.

Question 22 · Answer A

Television broadcasting uses geostationary satellites, which stay above the same point on the Earth so the receiving dish can stay fixed. The signals are carried by microwaves, which pass easily through the atmosphere and carry large amounts of information.

Question 23 · Answer A

Sound travels much faster in a solid such as steel than in air. The frequency is set by the source and does not change. Since speed = frequency multiplied by wavelength, and the speed increases while the frequency stays the same, the wavelength must also increase.

Question 24 · Answer A

The closeness of magnetic field lines represents the strength of the field. Where the lines are closest together, near the poles, the field is strongest. Where the lines are widely spaced the field is weaker.

Question 25 · Answer A

An electric field is a region in which an electric charge experiences a force. By convention, the direction of the electric field at a point is the direction of the force that would act on a small positive test charge placed there.

Question 26 · Answer A

Resistance is inversely proportional to the cross-sectional area of a wire. The cross-sectional area of a circular wire is proportional to the diameter squared. So resistance is inversely proportional to the diameter squared: doubling the diameter reduces the resistance to one quarter.

Question 27 · Answer A

In a series circuit the supply voltage is shared between the components. Two equal resistors share the 12 V equally, so each has a potential difference of 12 divided by 2 = 6.0 V.

Question 28 · Answer A

A diode, including an LED, only allows current to flow in one direction. It conducts and an LED lights only when it is forward biased, that is connected the correct way round so that current can pass. When reverse biased it blocks the current and stays off.

Question 29 · Answer A

The induced e.m.f. depends on how quickly the wire cuts magnetic field lines. Moving the wire faster cuts the field lines at a greater rate, so a larger e.m.f. is induced. A stronger magnet or more turns would also increase it.

Question 30 · Answer A

An a.c. generator uses a coil of wire rotating between magnetic poles, with slip rings to connect the coil to the external circuit. A split-ring commutator is used in a d.c. motor or dynamo to reverse connections; it is not part of an a.c. generator.

Question 31 · Answer A

A current in a long straight wire produces a magnetic field made up of concentric circles centred on the wire, lying in planes at right angles to the wire. The circles are closer together near the wire, where the field is strongest.

Question 32 · Answer A

The soft iron core concentrates and guides the changing magnetic field (flux) produced by the primary coil so that almost all of it passes through the secondary coil. This strong magnetic linkage allows an alternating voltage to be induced efficiently in the secondary coil. The core does not carry electric current between the coils.

Question 33 · Answer A

Most of the atom is empty space, so the great majority of alpha particles pass straight through the thin gold foil with little or no deflection. Only a very small number come close to the tiny, dense, positively charged nucleus and are deflected through large angles or bounced back.

Question 34 · Answer A

The nucleon number is the total number of protons and neutrons. So the number of neutrons = nucleon number minus proton number = 15 - 7 = 8.

Question 35 · Answer A

First subtract the background: source count rate = 520 - 40 = 480 counts per minute. In 4 hours there are 4 divided by 2 = 2 half-lives, so the source rate falls to 480 then 240 then 120 counts per minute. The detector also reads the background, so the reading is 120 + 40 = 160 counts per minute.

Question 36 · Answer A

In beta-minus decay a neutron changes into a proton and an electron, and the electron (the beta particle) is emitted. The proton number increases by 1, from 11 to 12, while the nucleon number stays at 24. So sodium-24 becomes magnesium-24 with proton number 12.

Question 37 · Answer A

Exposure to gamma radiation is reduced by keeping a large distance from the source, spending the shortest possible time near it, and placing dense shielding such as lead or thick concrete between the source and the person. Moving closer or staying longer would increase the exposure.

Question 38 · Answer A

TR is one day (the Earth spinning once), TM is about 27 days (the Moon orbiting the Earth) and TS is one year (the Earth orbiting the Sun). The shortest period is the day, TR, and the longest period is the year, TS.

Question 39 · Answer A

Light from distant galaxies is observed to be redshifted, meaning its wavelength is increased (shifted towards the red end of the spectrum). This is because those galaxies are moving away from us, and it is evidence that the Universe is expanding.

Question 40 · Answer A

The cosmic microwave background radiation was produced in the very early Universe with much shorter wavelengths. As the Universe expanded, the radiation was stretched, so its wavelength has increased over time and it is now in the microwave region. This means it had a shorter wavelength in the past.