May/June 2025 Paper 12 Worked Answers (IGCSE Physics 0625 Core)

40 questions · 40 marks · 45 minutes

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1. Question 1

   1 marksPeriod of a pendulum
   Step 1: The period $T$ is the time for one complete swing. Step 2: $T = \frac{\text{total time}}{\text{number of swings}} = \frac{30}{20} = 1.5\ \text{s}$.
   Method:

   Divide total time by number of swings.
   Examiner tips

   • Measure several swings and divide to get a more accurate period.

2. Question 2

   1 marksVolume of an irregular solid
   Step 1: Irregular solids cannot be measured directly with a ruler because they have no simple geometric shape. Step 2: Place the solid in a measuring cylinder containing a known volume of water. Step 3: The rise in water level equals the volume of the solid.
   Method:

   Identify the apparatus that measures liquid volume with a scale.
   Examiner tips

   • Water displacement is the standard method for irregular solids.

3. Question 3

   1 marksArea under a speed-time graph
   Step 1: On a speed-time graph, the area below the line is speed multiplied by time. Step 2: speed $\times$ time = distance, so the area represents the distance travelled.
   Method:

   Recall: gradient gives acceleration, area gives distance.
   Examiner tips

   • Graph slope = acceleration; graph area = distance.

4. Question 4

   1 marksExample of a force
   Step 1: Weight is the gravitational force on an object; it is measured in newtons, the SI unit of force. Step 2: Density (kg/m^3), mass (kg) and volume (m^3) are not forces.
   Method:

   Check the SI unit - newtons means it is a force.
   Examiner tips

   • If the unit is newtons, the quantity is a force.

5. Question 5

   1 marksFloating hollow balls
   Step 1: Density = mass / volume. P: $15/30 = 0.50\ \text{g/cm}^3$. Q: $25/30 \approx 0.83\ \text{g/cm}^3$. R: $35/30 \approx 1.17\ \text{g/cm}^3$. S: $45/30 = 1.50\ \text{g/cm}^3$. Step 2: An object floats if its density is less than the liquid's $0.95\ \text{g/cm}^3$. Step 3: P (0.50) and Q (0.83) are less than 0.95, so P and Q float.
   Method:

   Compute each density and compare with the liquid's.
   Examiner tips

   • Compare each ball's density to the liquid; lower density floats.

6. Question 6

   1 marksResultant force at constant speed
   Step 1: Constant speed in a straight line means zero acceleration. Step 2: Newton's second law: $F = ma$, so zero acceleration means zero resultant force. Step 3: Therefore there is no resultant force on the car.
   Method:

   Apply Newton's second law to constant-velocity motion.
   Examiner tips

   • Constant velocity in a straight line = zero resultant force.

7. Question 7

   1 marksTorque on a wrench
   Step 1: Moment $M = F \times d$, so $F = M/d$. Step 2: Convert $600\ \text{mm} = 0.60\ \text{m}$. Step 3: $F = 50 / 0.60 \approx 83\ \text{N}$.
   Method:

   Rearrange the moment equation and substitute SI values.
   Examiner tips

   • Always convert mm to m before using $M = Fd$.

8. Question 8

   1 marksWork done equation
   Step 1: Work done is force multiplied by the distance moved in the direction of the force. Step 2: $W = F d$ gives joules (newtons multiplied by metres).
   Method:

   Match the equation to the correct definition of work done.
   Examiner tips

   • Check units: $W$ in joules equals N multiplied by m.

9. Question 9

   1 marksEnergy resource using a boiler
   Step 1: Coal is burned in a boiler to heat water and produce high-pressure steam, which drives a turbine. Step 2: Tides, water in a dam (hydroelectric), and wind do not require boilers - they drive turbines directly using moving water or air.
   Method:

   Identify the fuel that needs to be burned to produce heat.
   Examiner tips

   • Fossil and nuclear plants use boilers and turbines; renewables usually drive turbines directly.

10. Question 10

    1 marksNames of change of state
    Step 1: Solid to liquid is melting; liquid to solid would be freezing. Step 2: Liquid to gas is boiling; gas to liquid would be condensing. Step 3: So the two changes are melting then boiling.
    Method:

    Use the heating direction to pick the two correct names.
    Examiner tips

    • Match each direction (heating or cooling) to the correct name.

11. Question 11

    1 marksWhy gases compress more than liquids
    Step 1: In a liquid, particles touch each other and almost no space lies between them. Step 2: In a gas, particles are far apart with large empty spaces between them. Step 3: Pushing the gas reduces those spaces, so the gas compresses. The liquid's particles are already touching, so it cannot be compressed.
    Method:

    Link compressibility to the size of the gaps between particles.
    Examiner tips

    • Always think about the spacing of particles when explaining compressibility.

12. Question 12

    1 marksGas pressure when volume increases
    Step 1: Pressure depends on how often (and how hard) particles strike the walls. Step 2: Constant temperature means the particles' average speed stays the same. Step 3: In a larger volume, each particle has more space and reaches the wall less often per second, so the pressure drops.
    Method:

    Use the kinetic model with constant temperature to explain falling pressure.
    Examiner tips

    • Constant temperature = constant average particle speed.

13. Question 13

    1 marksMass unchanged by temperature
    Step 1: Heating a solid makes it expand: its volume rises. Step 2: A higher volume with the same mass means a lower density. The hole in the nut and the length of the iron rod also grow. Step 3: Mass depends only on the amount of matter, which is unchanged when heating, so the mass of the coin stays the same.
    Method:

    Identify which property is unaffected by expansion.
    Examiner tips

    • Heating changes volume and density, but never mass.

14. Question 14

    1 marksGlass as a thermal conductor
    Step 1: Energy from the hot water reaches the hand through the glass wall by conduction. Step 2: Glass is a poor thermal conductor, so the energy travels slowly through it, giving a delay before the hand feels warm.
    Method:

    Link the delay to slow conduction through glass.
    Examiner tips

    • Glass and most insulators are poor thermal conductors.

15. Question 15

    1 marksConvection current
    Step 1: Heating makes the liquid expand: the same mass now fills a larger volume. Step 2: Density = mass / volume, so density falls. Step 3: The less dense warm liquid rises while cooler, denser liquid sinks, forming a convection current.
    Method:

    Link expansion to density change to convection.
    Examiner tips

    • Convection happens because hotter fluid is less dense.

16. Question 16

    1 marksConduction from a hotplate
    Step 1: With no air gap, the pan touches the hotplate, so the main route is conduction through the contact surface. Step 2: Metals are excellent thermal conductors, so the metal hotplate moves energy into the pan very effectively by conduction.
    Method:

    Match the absence of an air gap and the metal contact to conduction.
    Examiner tips

    • Identify the main heat transfer process based on whether the materials touch.

17. Question 17

    1 marksWave speed from frequency and wavelength
    Step 1: Frequency $f = 12 / 180 = 1/15\ \text{Hz} \approx 0.0667\ \text{Hz}$. Step 2: Wavelength $\lambda = 10\ \text{m}$. Step 3: Wave speed $v = f\lambda = 0.0667 \times 10 = 0.67\ \text{m/s}$.
    Method:

    Compute frequency from crests per second, then apply the wave equation.
    Examiner tips

    • Frequency = number of crests per second; speed = frequency multiplied by wavelength.

18. Question 18

    1 marksLongitudinal wave examples
    Step 1: Sound waves are longitudinal: the air particles vibrate along the direction the sound travels. Step 2: A pulse sent along a stretched spring (a slinky) where coils compress and stretch in the direction of travel is also longitudinal. Step 3: Water waves and a transverse rope pulse have vibrations at right angles to the direction of travel - they are transverse, not longitudinal.
    Method:

    Classify each example by the direction of the vibrations.
    Examiner tips

    • Test each example by checking the direction of vibration.

19. Question 19

    1 marksLight through a glass block
    Step 1: Air to glass: light slows down and bends towards the normal. Step 2: Glass to air: light speeds up and bends away from the normal. Step 3: Because the two glass faces are parallel, the bending at each face cancels in direction, so the emergent ray is parallel to the original incident ray (but shifted sideways).
    Method:

    Apply the refraction rule at each face and note parallel faces give a parallel emergent ray.
    Examiner tips

    • Parallel sides mean the emerging ray is parallel (but laterally shifted) compared with the incident ray.

20. Question 20

    1 marksFocal length of a converging lens
    Step 1: Use the thin lens equation $\frac{1}{f} = \frac{1}{u} + \frac{1}{v}$. Step 2: $\frac{1}{f} = \frac{1}{15} + \frac{1}{30} = \frac{2}{30} + \frac{1}{30} = \frac{3}{30} = \frac{1}{10}$. Step 3: Therefore $f = 10\ \text{cm}$.
    Method:

    Substitute and add fractions in the lens equation.
    Examiner tips

    • Always work in reciprocals when applying the lens equation.

21. Question 21

    1 marksTV remote control radiation
    Step 1: A typical TV remote uses a small LED on its front that emits infrared light. Step 2: Gamma rays, ultraviolet and X-rays are too high in energy and would be dangerous, expensive, or impossible to generate from a tiny battery.
    Method:

    Match the everyday device to the right band of the EM spectrum.
    Examiner tips

    • Infrared sits below visible red light - it is safe and easy to generate.

22. Question 22

    1 marksRadiations that cause cell damage
    Step 1: The higher the frequency of an EM wave, the more energy each photon carries. Step 2: Ultraviolet, X-rays and gamma rays carry enough energy to ionise atoms and damage cells. Step 3: Visible light and radio waves do not normally damage cells - so the harmful pair here is gamma rays and ultraviolet.
    Method:

    Pick the pair from the high-frequency end of the EM spectrum.
    Examiner tips

    • Anything to the right of visible light on the EM spectrum can ionise and harm cells.

23. Question 23

    1 marksAudible range as frequency
    Step 1: The human audible range is conventionally given as $20\ \text{Hz}$ to $20\,000\ \text{Hz}$. Step 2: Ultrasound is defined as sound with frequency greater than $20\,000\ \text{Hz}$. Step 3: So the scale labels frequencies in hertz.
    Method:

    Compare the values to the audible frequency range.
    Examiner tips

    • Remember the audible range: 20 Hz to 20 000 Hz.

24. Question 24

    1 marksBar magnet test on metal blocks
    Step 1: Repulsion is the only definite test for a magnet, because magnets repel only other magnets. Step 2: Block 2 shows repulsion, so block 2 must itself be a magnet. Step 3: Block 1 is only attracted, which any soft-magnetic material (such as iron) will show; so block 1 is not necessarily a magnet.
    Method:

    Apply the repulsion test - the only way to confirm a magnet.
    Examiner tips

    • Attraction can fool you - only repulsion proves it is a magnet.

25. Question 25

    1 marksCharging glass rod with silk
    Step 1: Only electrons (negative charges) can move during rubbing - protons stay in the nucleus. Step 2: The glass rod becomes positive, which means it has lost negative charge. Step 3: So electrons have moved from the glass rod to the silk cloth.
    Method:

    Identify what must move so that the glass loses negative charge.
    Examiner tips

    • Charging by friction always involves electron transfer.

26. Question 26

    1 marksElectric current in a metal wire
    Step 1: In a metal, the outer electrons are free to move; they carry the current. Step 2: When a potential difference is applied across the wire, these electrons drift slowly along its length. Step 3: Positive ions in the lattice stay in fixed positions, only vibrating slightly.
    Method:

    Identify which charges in a metal are mobile.
    Examiner tips

    • Current in a metal is a flow of free electrons.

27. Question 27

    1 markse.m.f. and p.d. share a unit
    Step 1: Both e.m.f. and potential difference are measured in volts. Step 2: Current is measured in amperes "electromotive force (e.m.f.) and potential difference (p.d.)" and charge in coulombs "potential difference (p.d.) and current", so they differ. Step 3: Resistance is measured in ohms ($\Omega$), which is different from volts.
    Method:

    Match each quantity to its SI unit and pick the matching pair.
    Examiner tips

    • List the SI units before answering this kind of question.

28. Question 28

    1 marksResistance from V and I
    Step 1: $R = V / I$. Step 2: $R = 10 / 0.050 = 200\ \Omega$.
    Method:

    Substitute V and I into $R = V/I$.
    Examiner tips

    • Convert mA to A before dividing if needed.

29. Question 29

    1 marksHeated thermistor in a series circuit
    Step 1: Heating a thermistor lowers its resistance. Step 2: Total resistance in the series circuit falls, so the current increases (ammeter rises). Step 3: Voltmeter reads $V = IR$ across the fixed resistor; $R$ is unchanged but $I$ rises, so the voltmeter reading also rises.
    Method:

    Track the thermistor's resistance, then use it to find the current and the resistor's p.d.
    Examiner tips

    • Heated thermistor = less resistance; treat the rest as a normal series circuit.

30. Question 30

    1 marksCurrent in a series circuit
    Step 1: Two $3.0\ \Omega$ resistors in series give $R_\text{total} = 6.0\ \Omega$. Step 2: Current $I = V / R = 12 / 6.0 = 2.0\ \text{A}$.
    Method:

    Add the resistors, then divide voltage by total resistance.
    Examiner tips

    • Series resistances add; then use Ohm's law.

31. Question 31

    1 marksChoosing a fuse rating
    Step 1: Operating current $I = P / V = 2700 / 240 = 11.25\ \text{A}$. Step 2: A fuse must be rated above the normal current but as low as practical. Step 3: $3\ \text{A}$, $5\ \text{A}$ and $10\ \text{A}$ would all blow when the vacuum cleaner runs; the next standard rating above $11.25\ \text{A}$ is $13\ \text{A}$.
    Method:

    Compute the working current and select the next fuse rating above.
    Examiner tips

    • Use $I = P/V$; pick the next standard fuse rating above it.

32. Question 32

    1 marksTransformer turns
    Step 1: Output voltage ($20\ \text{V}$) is less than input ($240\ \text{V}$), so the transformer steps voltage down. Step 2: Turns ratio: $\frac{N_p}{N_s} = \frac{V_p}{V_s}$, so $N_p = N_s \times \frac{V_p}{V_s} = 600 \times \frac{240}{20} = 600 \times 12 = 7200$.
    Method:

    Apply the turns ratio and pick the matching transformer type.
    Examiner tips

    • Step-down: primary has more turns than secondary.

33. Question 33

    1 marksNegative ion to neutral atom
    Step 1: A negative ion has more electrons than protons. Step 2: To make it neutral, the extra electrons must be removed; the ion has to lose electrons.
    Method:

    Identify why the ion is negative, then reverse it.
    Examiner tips

    • Protons stay in the nucleus; only electrons move in everyday processes.

34. Question 34

    1 marksNeutrons in nitrogen-15
    Step 1: The top number is the mass number $A = 15$ (total nucleons). Step 2: The bottom number is the proton number $Z = 7$. Step 3: Neutrons $N = A - Z = 15 - 7 = 8$.
    Method:

    Read A and Z from the symbol and subtract.
    Examiner tips

    • Subtract Z from A to find N.

35. Question 35

    1 marksNatural background radiation sources
    Step 1: Natural sources of background radiation include rocks and building materials, food, drink, the human body, and radon gas from the ground; cosmic rays from space are also natural. Step 2: Nuclear power stations and mobile phones are man-made and are not natural background radiation. Step 3: Only one list has zero man-made entries.
    Method:

    Eliminate any list containing a man-made source.
    Examiner tips

    • Anything you can build or manufacture is not natural background radiation.

36. Question 36

    1 marksComparing alpha, beta, gamma emissions
    Step 1: Alpha particles are heavy and doubly charged, so they ionise atoms strongly over a short range. Step 2: Gamma rays (not beta) are the most penetrating and they are electromagnetic waves. Step 3: Beta particles are fast electrons; they are particles, not part of the EM spectrum.
    Method:

    Use the standard rankings of ionising power and penetration.
    Examiner tips

    • Order of ionising power: alpha > beta > gamma. Order of penetration: alpha < beta < gamma.

37. Question 37

    1 marksLead as a radiation shield
    Step 1: Lead is a dense metal whose atoms absorb the energy of nuclear radiation, especially gamma rays. Step 2: Radiation cannot be neutralised, repelled or dissolved - only absorbed.
    Method:

    Pick the only mechanism that physically blocks radiation.
    Examiner tips

    • Lead is dense and ideal for absorbing gamma rays.

38. Question 38

    1 marksDay and night vs seasons
    Step 1: One day equals one full spin of the Earth on its axis, so the day and night cycle is caused by Earth's rotation. Step 2: Seasons arise because the Earth's tilted axis points the same way through a full orbit of the Sun; the cycle period equals the orbital period (1 year). Step 3: Moon orbits the Earth in about 1 month and gives us lunar phases, not seasons.
    Method:

    Pair the two periods with the matching motion.
    Examiner tips

    • Match each cycle to the right Earth motion.

39. Question 39

    1 marksGravitational field strength
    Step 1: A larger planet mass gives a stronger gravitational field at the surface. Step 2: Gravitational field strength falls as the distance from the planet grows.
    Method:

    Apply the qualitative rules for $g$.
    Examiner tips

    • Gravitational field strength depends on the mass of the body and the distance from it.

40. Question 40

    1 marksSolar emission band
    Step 1: The Sun's spectrum peaks in the visible, with significant amounts in the infrared (the warmth we feel) and the ultraviolet (which causes sunburn). Step 2: Microwaves, radio waves and X-rays make up much smaller portions of the Sun's emission.
    Method:

    Pick the band on either side of visible light that the Sun also radiates strongly.
    Examiner tips

    • Sunlight warms you because of its infrared content.