May/June 2025 Paper 11 Worked Answers (IGCSE Physics 0625 Core)

40 questions · 40 marks · 45 minutes

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1. Question 1

   1 marksReading a measuring cylinder
   Step 1: The volume is read at the level of the meniscus. Step 2: The midpoint between $14\ \text{cm}^3$ and $18\ \text{cm}^3$ is $\frac{14+18}{2} = 16\ \text{cm}^3$. Step 3: The volume is therefore $16.0\ \text{cm}^3$.
   Method:

   Identify the labelled marks above and below the meniscus, then take their midpoint.
   Examiner tips

   • Look at the actual labelled values on the scale before assuming each line is 1 cm^3.

2. Question 2

   1 marksSpeed and velocity definitions
   Step 1: Speed is a scalar quantity - it has size only. Step 2: Velocity is a vector quantity - it has size and direction. Step 3: So velocity is the speed of an object in a stated direction.
   Method:

   Recall that velocity adds a direction to speed; pick the statement that captures this.
   Examiner tips

   • Remember that velocity is a vector - it needs a direction as well as a number.

3. Question 3

   1 marksAverage speed comparison
   Step 1: Average speed = distance / time. Step 2: Race 1: $100/12 \approx 8.33\ \text{m/s}$. Race 2: $150/17 \approx 8.82\ \text{m/s}$. Race 3: $200/25 = 8.0\ \text{m/s}$. Step 3: From lowest to highest: race 3 (8.0), race 1 (8.33), race 2 (8.82), so the order is 3, 1, 2.
   Method:

   Compute each race's average speed, then arrange from smallest to largest.
   Examiner tips

   • Calculate each speed first; do not guess from the distances alone.

4. Question 4

   1 marksWeight from mass
   Step 1: Weight = mass $\times$ gravitational field strength, so $W = mg$. Step 2: Substitute: $W = 2.00 \times 9.8 = 19.6\ \text{N}$.
   Method:

   Multiply the mass by the gravitational field strength.
   Examiner tips

   • Keep units clear: kg multiplied by N/kg gives N.

5. Question 5

   1 marksFloating and density
   Step 1: An object floats if its density is less than the liquid's density. Step 2: Density = mass / volume. W: $2.0/3.0 \approx 0.67\ \text{g/cm}^3$. X: $1.0/0.5 = 2.0\ \text{g/cm}^3$. Y: $6.0/4.0 = 1.5\ \text{g/cm}^3$. Z: $9.0/6.0 = 1.5\ \text{g/cm}^3$. Step 3: Only W has a density below $1.4\ \text{g/cm}^3$, so only W floats.
   Method:

   Work out each density, then compare with the liquid's density.
   Examiner tips

   • Density compares mass to volume - the answer is rarely the lightest object.

6. Question 6

   1 marksTerminal velocity from drag
   Step 1: As the car speeds up, the resistive forces grow because they are proportional to the speed. Step 2: The driving force is constant, so the resultant force shrinks. Step 3: When the resistive forces equal the driving force, the resultant is zero. Step 4: Zero resultant means zero acceleration, so the speed stays at its maximum value.
   Method:

   Identify that the resistive forces grow until they cancel the driving force, then the acceleration is zero.
   Examiner tips

   • Maximum speed is the point where resultant force is zero, not where it is negative.

7. Question 7

   1 marksElastic potential energy store
   Step 1: Springs that are squashed or stretched gain elastic potential energy. Step 2: The mattress springs are compressed by the person's weight, so the energy stored elastically in the springs increases.
   Method:

   Match the action (squashing a spring) to the elastic store.
   Examiner tips

   • Squashed or stretched objects store elastic potential energy.

8. Question 8

   1 marksEnergy resource without chemical store
   Step 1: Biofuel, coal and oil release energy by burning - their store is chemical energy in molecular bonds. Step 2: Nuclear fuel releases energy from the nucleus of the atom (fission), not from chemical bonds. Step 3: So nuclear fuel does not have a chemical energy store.
   Method:

   Rule out the three that burn (chemical) and pick the remaining one.
   Examiner tips

   • Anything that is burned to release energy stores chemical energy.

9. Question 9

   1 marksWork done against gravity
   Step 1: Total mass = $20 \times 1.2 = 24\ \text{kg}$. Step 2: Total weight = $24 \times 9.8 = 235.2\ \text{N}$. Step 3: Work done against gravity = force $\times$ height = $235.2 \times 15 = 3528\ \text{J} \approx 3500\ \text{J}$.
   Method:

   Find total mass, then total weight, then multiply by height.
   Examiner tips

   • Multiply the number of tiles by the mass of one tile before finding the weight.

10. Question 10

    1 marksPressure on the ground
    Step 1: Pressure = force / area. Step 2: A larger force (weight) and a smaller area both increase pressure. Step 3: Therefore the change that always increases pressure is to increase the weight while decreasing the contact area.
    Method:

    Use $p = F/A$ and pick the option that increases F and decreases A.
    Examiner tips

    • Apply $p = F/A$ in your head: which direction does each option move it?

11. Question 11

    1 marksMelting point from heating
    Step 1: A pure substance melts at a fixed temperature, shown by a flat region on a heating curve. Step 2: Y's plateau is at $50\ ^\circ\text{C}$ and X's plateau is at $80\ ^\circ\text{C}$. Step 3: Since the plateaus are the melting points, Y has the lower melting point.
    Method:

    Match each plateau to a melting point, then compare.
    Examiner tips

    • Always look at where the flat region sits on the temperature axis.

12. Question 12

    1 marksLiquid to gas property change
    Step 1: Both liquids and gases are fluids - their particles can move past each other, so both can flow. Step 2: Shape, volume and compressibility all change when a liquid becomes a gas: a gas fills its container and is much easier to compress. Step 3: The only property unchanged is the ability to flow.
    Method:

    Eliminate properties that change at the liquid-gas boundary.
    Examiner tips

    • Both liquids and gases are fluids - they share the ability to flow.

13. Question 13

    1 marksParticle spacing in solid vs gas
    Step 1: Solids have tightly packed particles with almost no space between them, so a solid resists being squeezed smaller. Step 2: Gases have particles far apart with large gaps; the gaps can be reduced, so a gas is easily compressed. Step 3: The key difference is the spacing of the particles.
    Method:

    Link the close packing of solids to the hard-to-compress observation.
    Examiner tips

    • Compressibility is mostly about empty space between particles.

14. Question 14

    1 marksGas pressure when volume increases
    Step 1: Pressure on the syringe wall comes from gas particles striking it. Step 2: When the volume is larger, the same particles are spread over more space, so each piece of wall is hit less often per second. Step 3: Fewer collisions per second means lower pressure.
    Method:

    Use the particle model: bigger volume spreads particles out, so they hit the wall less often.
    Examiner tips

    • Constant temperature means each particle's speed is unchanged - only the collision rate changes with volume.

15. Question 15

    1 marksEvaporation
    Step 1: Molecules in a liquid have a range of speeds and so a range of kinetic energies. Step 2: Only the molecules near the surface that have enough kinetic energy can break free from the attractive forces. Step 3: It is the most energetic molecules that escape, leaving the slower ones behind (so the remaining liquid cools).
    Method:

    Match the cooling effect of evaporation to high-energy molecules leaving the surface.
    Examiner tips

    • Evaporation cools the liquid because the fastest molecules leave.

16. Question 16

    1 marksThermal conductors comparison
    Step 1: A shorter time for the pin to fall means heat reached the cold end faster, so the material is a better thermal conductor. Step 2: X (30 s) takes less time than Y (80 s), so X is the better conductor of the two. Step 3: All other comparisons fail: Y, Z and Z again take longer than the rod they are compared with.
    Method:

    Rank by time taken; the rod with the smaller time is the better conductor.
    Examiner tips

    • Translate the time into conductivity: shorter time = better conductor.

17. Question 17

    1 marksBest thermal emitter
    Step 1: Dark, matt surfaces are the best emitters and absorbers of thermal radiation. Step 2: Shiny, light-coloured surfaces emit (and absorb) thermal radiation the worst. Step 3: Of the four options, dull black is the darkest and most matt, so it emits thermal radiation at the highest rate.
    Method:

    Apply the rule: dull-and-dark is the best emitter.
    Examiner tips

    • Best emitter = best absorber = dull and dark.

18. Question 18

    1 marksWave equation
    Step 1: Frequency = number of waves / time = $4.0/10 = 0.40\ \text{Hz}$. Step 2: Wave equation: $v = f\lambda$, so $\lambda = v/f$. Step 3: $\lambda = 2.0 / 0.40 = 5.0\ \text{m}$.
    Method:

    Compute frequency from the data, then divide speed by frequency.
    Examiner tips

    • Frequency is waves per second, not waves total.

19. Question 19

    1 marksTransverse wave example
    Step 1: In a transverse wave, the vibrations are perpendicular (at right angles) to the direction the wave travels. Step 2: Water waves are transverse: the surface moves up and down while the wave moves horizontally. Step 3: Sound waves are longitudinal, with vibrations parallel to the direction of travel.
    Method:

    Recall the definitions of transverse and longitudinal waves and match the example.
    Examiner tips

    • Memorise: transverse = perpendicular; longitudinal = parallel.

20. Question 20

    1 marksWavefront and wavelength on ripples
    Step 1: A wavefront is a line joining points on a wave that are all at the same point in their cycle (for ripples, the curved crest line). Step 2: The wavelength is the perpendicular distance between two such wavefronts. Step 3: So X (the crest line) is a wavefront, and Y (gap between crests) is the wavelength.
    Method:

    Match the description of X and Y to the standard definitions of wavefront and wavelength.
    Examiner tips

    • Amplitude is a height, not a distance between rings.

21. Question 21

    1 marksClock seen in plane mirror
    Step 1: A vertical mirror reflects left and right but not top and bottom. The number 12 stays at the top and 6 at the bottom; the 3 and 9 swap. Step 2: Hour: reflected hour 5 corresponds to actual hour $12 - 5 = 7$. Step 3: Minute: reflected 45 min (hand at 9) corresponds to actual $60 - 45 = 15$ min (hand at 3). Step 4: Actual time = $7{:}15$.
    Method:

    Subtract the apparent hour from 12, and the apparent minutes from 60.
    Examiner tips

    • Mirror reflection in a vertical mirror swaps positions across the 12 to 6 line.

22. Question 22

    1 marksAngles of reflection and refraction
    Step 1: Angle of reflection equals angle of incidence, so it is also $40\ ^\circ$ to the normal. Step 2: Light slows down when entering glass from air, so it bends towards the normal. Step 3: That means the angle of refraction is smaller than the angle of incidence: less than $40\ ^\circ$.
    Method:

    Apply law of reflection and the rule that light bends towards the normal entering glass.
    Examiner tips

    • Always measure angles from the normal, not from the surface.

23. Question 23

    1 marksLoudness and pitch of sound
    Step 1: Loudness depends on amplitude: larger amplitude means louder sound. Step 2: Pitch depends on frequency: higher frequency means higher pitch. Step 3: If both amplitude and frequency rise, loudness rises and pitch rises.
    Method:

    Use the two-pair rule: bigger amplitude = louder; bigger frequency = higher pitch.
    Examiner tips

    • Remember the two pairs: amplitude-loudness and frequency-pitch.

24. Question 24

    1 marksSound and ultrasound facts
    Step 1: The human audible range is $20\ \text{Hz}$ to $20\,000\ \text{Hz}$. Step 2: Ultrasound has frequencies above $20\,000\ \text{Hz}$ but travels at the same speed as audible sound in air, about $330\ \text{m/s}$.
    Method:

    Eliminate options that change well-known speeds or frequency limits.
    Examiner tips

    • Remember the two key facts: audible range and that ultrasound travels at normal sound speed.

25. Question 25

    1 marksSoft iron and steel as magnets
    Step 1: Soft iron is a soft magnetic material: it magnetises and demagnetises easily. Step 2: Steel is a hard magnetic material: once magnetised, it retains its magnetism (hard to demagnetise). Step 3: So soft iron is easy and steel is hard to demagnetise.
    Method:

    Match the words soft and hard in the materials to their behaviour.
    Examiner tips

    • Soft magnetic material = soft iron; hard magnetic material = steel.

26. Question 26

    1 marksCharges on rods near a negative rod
    Step 1: Unlike charges attract, like charges repel. Step 2: X is attracted by a negative rod, so X must be the opposite sign: positive. Step 3: Y is repelled by the negative rod, so Y must be the same sign: negative.
    Method:

    Apply the attract or repel rule to each rod separately.
    Examiner tips

    • Pin the rule: like repels, unlike attracts.

27. Question 27

    1 marksGreatest electrical power
    Step 1: Power $P = V \times I$. Step 2: Car headlight: $12 \times 3.0 = 36\ \text{W}$. Cooling fan: $110 \times 0.40 = 44\ \text{W}$. Electric spark generator: $400\,000 \times 0.000\,1 = 40\ \text{W}$. Mains lamp: $240 \times 0.20 = 48\ \text{W}$. Step 3: The mains lamp has the largest power, $48\ \text{W}$.
    Method:

    Calculate $V \times I$ for each device using SI units.
    Examiner tips

    • Always convert kV to V and mA to A before multiplying.

28. Question 28

    1 marksDouble-insulated appliance
    Step 1: A double-insulated appliance has the live parts insulated and is also surrounded by a second layer of insulation, often the outer plastic casing. Step 2: This means the casing cannot become live and the appliance does not need an earth wire. Step 3: Fuses and neutral connections are still required for normal operation.
    Method:

    Recall that double insulation makes the case safe even with a fault.
    Examiner tips

    • Double insulation is a substitute for the earth wire, not for the fuse.

29. Question 29

    1 marksDefinition of magnetic field
    Step 1: A magnetic field is defined as a region in which a magnetic pole feels a force. Step 2: Most objects, most metals (such as copper or aluminium), and stationary charges do not feel this force, so only magnetic poles are the right test object.
    Method:

    Pick the test object that is the definition - a magnetic pole.
    Examiner tips

    • Magnetic field acts on magnetic poles - moving charges feel a force too, but stationary ones do not.

30. Question 30

    1 marksCharging by friction
    Step 1: Only electrons can move easily between materials when they are rubbed together; protons and neutrons stay locked in the nucleus. Step 2: Losing electrons leaves a net positive charge. Step 3: Therefore the plastic rod becomes positive because electrons have been transferred away from it.
    Method:

    Recall that friction moves electrons; identify the only one that fits both pieces of evidence.
    Examiner tips

    • Charging by friction always involves electrons moving between surfaces.

31. Question 31

    1 marksSeries cells and resistors
    Step 1: Cells in series add their e.m.f.s, so total e.m.f. = $1.5 + 1.5 + 1.5 = 4.5\ \text{V}$. Step 2: Resistors in series add their resistances, so total resistance = $20 + 20 = 40\ \Omega$.
    Method:

    Add e.m.f.s, add resistances.
    Examiner tips

    • Series: add; parallel: combine using the reciprocal rule for resistors and keep one cell's e.m.f.

32. Question 32

    1 marksTurning effect on current coil
    Step 1: Force on each wire in the coil = $BIL$, so it grows with the current. Step 2: The turning effect also grows with the number of turns because more wires share the same force. Step 3: Increasing both the current and the number of turns must therefore increase the turning effect.
    Method:

    Identify the two changes that each raise the force on the coil.
    Examiner tips

    • Turning effect rises with current, field strength, area, and number of turns.

33. Question 33

    1 marksMagnetic field around a conductor
    Step 1: The size of the magnetic field around a straight wire grows with the size of the current. The current doubles from $3.0$ to $6.0\ \text{A}$, so the field strength rises. Step 2: Reversing the current direction reverses the direction in which the field lines circle the wire. Step 3: Combining both effects: stronger field, opposite direction.
    Method:

    Apply both rules separately and combine.
    Examiner tips

    • Field strength tracks current size; field direction tracks current direction.

34. Question 34

    1 marksBackground radiation other sources
    Step 1: All contributions to background radiation must add to $100\%$. Step 2: Sum of the four listed sources = $48 + 13 + 10 + 11 = 82\%$. Step 3: Remaining sources = $100 - 82 = 18\%$.
    Method:

    Sum the listed percentages, then take from 100.
    Examiner tips

    • All contributions must sum to 100%.

35. Question 35

    1 marksGamma decay (proton number unchanged)
    Step 1: Alpha emission removes 2 protons (proton number drops by 2). Step 2: Beta-minus emission converts a neutron into a proton (proton number rises by 1). Step 3: Gamma emission carries away energy as electromagnetic radiation; the nucleus loses no protons or neutrons, so the proton number is unchanged.
    Method:

    Use the effect of each emission on Z to eliminate options.
    Examiner tips

    • Gamma decay is the only emission with no charge and no nucleons.

36. Question 36

    1 marksIons from losing electrons
    Step 1: A neutral atom contains equal numbers of protons and electrons. Step 2: Losing one or more electrons leaves the atom with more protons than electrons, so it becomes positive. Step 3: A charged atom is called an ion, so atoms become positively charged ions.
    Method:

    Track the charge change as electrons leave.
    Examiner tips

    • Atoms - lose electrons - become positive ions.

37. Question 37

    1 marksProtons from atomic number
    Step 1: Atomic number Z = number of protons in the nucleus. Step 2: For this isotope, Z = 36, so the nucleus contains 36 protons. (Mass number $A = 78$ would give 78 minus 36 = 42 neutrons, which is not asked.)
    Method:

    Read off the atomic number directly.
    Examiner tips

    • Atomic number = protons; mass number = protons + neutrons.

38. Question 38

    1 marksEarth spin and orbit times
    Step 1: A day, the time the Earth takes to spin once on its axis, is about $24$ hours. Step 2: A year, the time for one full orbit of the Sun, is about $365$ days. Step 3: So the correct pair is $24$ hours for the spin and $365$ days for the orbit.
    Method:

    Translate spin to day and orbit to year.
    Examiner tips

    • Day = spin on axis; year = orbit around the Sun.

39. Question 39

    1 marksRedshift and the Big Bang
    Step 1: Redshift means the observed wavelength is longer than the emitted wavelength. Step 2: Light from galaxies moving away from us is redshifted; light from those moving towards us is blueshifted. Step 3: The Big Bang theory says the whole Universe expanded from a very small point and has been expanding for about $14$ billion years.
    Method:

    Define redshift correctly, then check each statement.
    Examiner tips

    • Redshift = stretched wavelength; blueshift = compressed.

40. Question 40

    1 marksMilky Way galaxy
    Step 1: The Milky Way is the galaxy that contains the Sun and roughly $100$ billion other stars. Step 2: It is not inside the Solar System - the Solar System is one tiny part of the Milky Way. Step 3: Some of the stars we can see in the sky are in the Milky Way, but the Milky Way as a whole is the galaxy itself, not just the stars we can see.
    Method:

    Pick the option at the correct scale - a galaxy, not a Solar System feature.
    Examiner tips

    • Galaxy = collection of billions of stars.