IGCSE Physics 0625/23 October/November 2025 Past Paper with Answers

Question 1

A pendulum swings past a fixed marker. When it first passes the marker, a timer shows 0 s. The pendulum passes the same marker from the same direction 15 more times. The timer reads 60 s when the pendulum makes its final pass. What is the period of oscillation?

1. 4.0 s
2. 4.4 s
3. 7.5 s
4. 12 s

Question 2

A vehicle decelerates uniformly from its initial speed to rest in 10 s. The deceleration is $5.0 \text{ m/s}^2$. What is the average speed of the vehicle during this time?

1. 25 m/s
2. 10 m/s
3. 50 m/s
4. 5.0 m/s

Question 3

A ball is released from rest and falls through air, eventually reaching terminal velocity. Which row correctly describes the velocity of the ball and its acceleration during the whole fall?

1. velocity increases then becomes constant; acceleration positive then zero
2. velocity increases then decreases; acceleration positive then negative
3. velocity increases then decreases; acceleration positive then zero
4. velocity increases then constant; acceleration positive then negative

Question 4 · Answer A

A balance compares the unknown mass against known masses (or uses calibrated springs/strain gauges). A protractor measures angles, a stop-watch measures time, and a voltmeter measures potential difference. None of the other three instruments measure mass.

Question 5 · Answer A

Liquids that do not mix layer according to density: the least dense floats on top. J has the lowest density (1.2), so it is on top. K (1.8) is in the middle. L (2.4) is densest and sinks to the bottom. Order top to bottom: J, K, L.

Question 6 · Answer A

The two forces are equal in magnitude and opposite in direction, so the resultant force is zero. By Newton's first law, a zero resultant force means no change in velocity, so the vehicle continues at constant speed in the same direction.

Question 7 · Answer A

Anticlockwise moment (left) = 4.0 N x 3.0 m = 12 N m. Clockwise moment (right) = 6.0 N x 2.0 m = 12 N m. The moments are equal so the principle of moments is satisfied and the beam is in equilibrium.

Question 8 · Answer A

Impulse = force x time = 160 x 0.050 = 8.0 N s. By the impulse-momentum theorem, impulse = mass x change in velocity, so mass = 8.0 / 20 = 0.40 kg. Average acceleration = force / mass = 160 / 0.40 = 400 m/s^2.

Question 9 · Answer A

A car engine burns chemical fuel (petrol or diesel) and converts that chemical energy into kinetic energy of the moving vehicle. An a.c. generator converts kinetic energy to electrical energy. A battery-powered torch converts chemical energy to light (and thermal) energy. A wind-up clock converts elastic (strain) energy to kinetic energy.

Question 10 · Answer A

Wind is caused by unequal heating of the Earth's surface by the Sun, which creates convection currents in the atmosphere. Geothermal energy comes from heat inside the Earth (radioactive decay and residual formation heat). Nuclear energy comes from fission of uranium nuclei. Tidal energy comes from gravitational interactions dominated by the Moon, not the Sun.

Question 11 · Answer A

Lowering temperature reduces the average kinetic energy of gas particles; they move more slowly. Slower particles travel less distance per second, so they hit the container walls less frequently. Fewer collisions per second means a smaller force on the walls and therefore lower pressure.

Question 12 · Answer A

Using Boyle's law at constant temperature: $p_1 V_1 = p_2 V_2$. So $p_2 = 150 \times 20 / 12 = 250 \text{ kPa}$. Change in pressure = 250 - 150 = 100 kPa.

Question 13 · Answer A

Using $E = mc\Delta T$: $E = 2000 \times 0.200 \times 5 = 2000 \text{ J}$. Note that mass must be converted from grams to kilograms: 200 g = 0.200 kg.

Question 14 · Answer A

Changes that go from a lower-energy state to a higher-energy state require energy input. Melting (J) breaks bonds in a solid, requiring energy. Vaporisation (K) breaks bonds in a liquid, requiring energy. Condensation (L) and freezing (M) both release energy as particles form stronger bonds.

Question 15 · Answer A

Metals are good conductors because they contain free (delocalised) electrons. These electrons gain kinetic energy at the hot end and move through the lattice, transferring energy to cooler regions. The positive metal ions are held in a fixed lattice; they vibrate but do not move from place to place.

Question 16 · Answer A

When air is heated it expands, so the same mass occupies a larger volume: its density decreases. This less-dense warm air experiences a net upward buoyancy force and rises to the top of the room. Cooler, denser air sinks to the bottom. This convection current means warmer air accumulates near the ceiling.

Question 17 · Answer A

A star radiates power from its entire surface. If two stars emit the same total power but star P has a larger surface area, then P radiates less power per unit area. The power radiated per unit area increases with temperature (Stefan-Boltzmann law), so the star with lower power per unit area must have a lower surface temperature. Therefore P is cooler than Q.

Question 18 · Answer A

Diffraction (spreading) is most pronounced when the gap width is comparable to or smaller than the wavelength, and least when the gap is much wider than the wavelength. The wavelength here is 2 cm. A 10 cm gap is five times the wavelength, so the waves pass through almost as a straight beam with the least spreading. The 1 cm and 2 cm gaps, being smaller than or equal to the wavelength, produce the most diffraction.

Question 19 · Answer A

By the law of reflection, the angle of reflection equals the angle of incidence, both measured from the normal to the mirror. Angle of reflection = 35°. The angle between the incident ray and the mirror surface is the complement of the angle of incidence: 90° - 35° = 55°.

Question 20 · Answer A

Refractive index $n = c / v = 3.0 \times 10^8 / 2.25 \times 10^8 = 1.333$. Snell's law: $n_1 \sin\theta_1 = n_2 \sin\theta_2$, so $\sin\theta_2 = \sin 40° / 1.333 = 0.6428 / 1.333 = 0.482$. Therefore $\theta_2 = \arcsin(0.482) = 28.8° \approx 28°$. The ray bends towards the normal when entering a denser medium.

Question 21 · Answer A

In a short-sighted eye the lens is too powerful (or the eyeball too long), so parallel rays from a distant object converge to a focus before reaching the retina. A diverging (concave) lens pre-diverges the rays so that the eye then focuses them correctly onto the retina.

Question 22 · Answer A

All electromagnetic waves travel at the same speed in a vacuum ($3.0 \times 10^8 \text{ m/s}$). Gamma rays have the shortest wavelength (and highest frequency) in the EM spectrum. Radio waves have the longest wavelength and lowest frequency. Visible light is in between.

Question 23 · Answer A

Amplitude controls loudness: larger amplitude means louder sound. Frequency controls pitch: lower frequency means lower pitch. When amplitude increases, the sound gets louder. When frequency decreases, the pitch drops. The result is a louder sound with a lower pitch.

Question 24 · Answer A

Inside a solenoid the magnetic field lines are parallel and closely spaced, indicating a strong, uniform field. Outside the ends the field lines diverge (spread out), so the field is weaker. The field at the centre (Q) is therefore greater than at the outside positions P and R, which are approximately equal to each other.

Question 25 · Answer A

When two materials are rubbed together, electrons (not protons) are transferred. Protons are locked in atomic nuclei and do not move. The glass rod becomes positively charged because it loses electrons to the silk cloth, leaving the rod with fewer electrons than protons.

Question 26 · Answer A

By convention, conventional current flows from the positive terminal through the external circuit to the negative terminal. In reality, electrons (negative charge) flow in the opposite direction: from the negative terminal to the positive terminal through the external circuit.

Question 27 · Answer A

Electromotive force (e.m.f.) is defined as the energy supplied by a source (battery or generator) per unit charge that passes through it in driving charge around the complete circuit. Current is the charge per unit time; potential difference is the energy transferred per unit charge between two points; power is the energy per unit time.

Question 28 · Answer A

Energy transferred $E = V \times I \times t$. Convert: current 50 mA = 0.050 A; time 2.0 min = 120 s. $E = 6.0 \times 0.050 \times 120 = 36 \text{ J}$.

Question 29 · Answer A

A lamp only lights when a complete, unbroken conducting path exists from one terminal of the battery, through the lamp, and back to the other terminal. Any break in the circuit (open switch, disconnected wire) prevents current from flowing and the lamp does not light.

Question 30 · Answer A

By Kirchhoff's first law, the total current entering a junction equals the total current leaving it. Total current entering the parallel section = 6.0 A. Branch 1 carries 4.0 A. Therefore branch 2 carries 6.0 - 4.0 = 2.0 A.

Question 31 · Answer A

When the rheostat resistance is at maximum, almost all the supply voltage drops across the rheostat and nearly 0 V appears across the lamp. When the rheostat is at 0 ohms, the full 9.0 V appears across the lamp. So the lamp p.d. can vary from 0 V to 9.0 V by adjusting the rheostat.

Question 32 · Answer A

By Lenz's law, the force on the induced current acts in a direction that opposes the change causing the induction. The wire is moving downward, so the force on the induced current acts upward, opposing the downward motion. This is consistent with conservation of energy.

Question 33 · Answer A

Mean background count = (160 + 170 + 150) / 3 = 480 / 3 = 160 counts per 10 minutes = 16 counts/min. Corrected count rate = measured rate - background rate = 500 - 16 = 484 counts/min.

Question 34 · Answer A

A magnetic field exerts a force on moving charged particles ($F = Bqv$). Gamma rays carry no charge, so the field exerts no force and they travel in a straight line. Alpha particles (charge +2e) and beta particles (charge -e) are oppositely charged, so the magnetic force acts in opposite directions, deflecting them in opposite directions. Alpha particles (greater mass and charge) follow a less curved path than the lighter beta particles.

Question 35 · Answer A

All radioactive decay, whether alpha or beta, is both spontaneous (it occurs without any external trigger such as temperature, pressure, or chemical state) and random (it is impossible to predict exactly when a particular nucleus will decay or which nucleus in a sample will be next). These properties apply equally to alpha and beta decay.

Question 36 · Answer A

In beta-minus decay, a neutron inside the nucleus is transformed into a proton. The electron produced in this process is immediately emitted as the beta particle. This increases the proton number (atomic number) by 1, while the nucleon number stays the same because one neutron has become one proton.

Question 37 · Answer A

Alpha particles are stopped by paper or a few centimetres of air. Beta particles are stopped by a few millimetres of aluminium. Gamma rays are the most penetrating and require several centimetres of lead or metres of concrete to be adequately absorbed. Since the container must stop all three, it must be made of thick lead, which stops even gamma rays (and therefore also stops alpha and beta).

Question 38 · Answer A

The satellite travels one complete orbit (a circle of circumference $2\pi r$) at constant orbital speed $v$. Period $T = \frac{2\pi r}{v} = \frac{2\pi \times 8.0 \times 10^6}{4000} = \frac{5.027 \times 10^7}{4000} = 12 566 \text{ s}$. Converting: $12566 / 60 = 209.4 \text{ min} \approx 3 \text{ h } 29 \text{ min}$.

Question 39 · Answer A

The Sun consists mainly of hydrogen (about 73%) and helium (about 25%), with trace amounts of heavier elements. At its surface temperature of about 5800 K, Wien's law places the peak of its emission spectrum at about 500 nm, which is in the green part of the visible spectrum. The overall emission covers visible light and near-infrared/near-ultraviolet. X-rays are emitted mainly by the corona (very high temperature), not the photosphere.

Question 40 · Answer A

When a massive star explodes as a supernova, it ejects its outer layers into space, forming an expanding cloud of gas called a nebula (or supernova remnant). The collapsed core that remains becomes a neutron star (if the mass is below about 3 solar masses) or a black hole for more massive cores. White dwarfs are the remnants of low-mass stars that do not explode as supernovae. Red supergiants are the pre-supernova stage, not a product of the supernova.