Mark Scheme

Section A: 1. A; 2. B; 3. B; 4. B; 5. B; 6. C. (6)

7 (a) p = mv = 1500 × 12 = 18 000 kg m/s (1 method, 1 answer). (b) total momentum before = total momentum after, in a closed system (1). (c) the crumple zone increases the time of the collision (1); for the same change in momentum, a longer time means a smaller force (1); reducing the force on the passengers (1). (6)

8 (a) moment = F × d = 40 × 0.5 = 20 Nm (1 method, 1 answer). (b) total clockwise moment = total anticlockwise moment (1). (c) greater depth → greater weight of liquid above (1) → greater pressure (1). (5)

9 (a) v = fλ = 25 × 8 = 200 m/s (1 method, 1 answer). (b) light slows down (1); bends towards the normal (1). (c) parallel rays are refracted to meet at the principal focus (1); a real image can be projected onto a screen (1); it forms where the rays actually meet (1). (7)

10 (a) matt black surfaces (1). (b) it emits radiation at the same rate as it absorbs it (1); so there is no net change in energy/temperature (1). (3)

11 (a) move a wire/magnet relative to each other / change the field through a coil (1); this induces a potential difference (1). (b) any two: move faster; stronger magnet; more turns; larger coil area (2). (c) Vp/Vs = Np/Ns → 230/Vs = 100/500 (1); Vs = 230 × 5 (1) = 1150 V (1). (7)

12 (a) gravity pulls a nebula (dust and gas) together (1); it heats up forming a protostar (1); fusion begins → main sequence star (1). (b) inward gravity is balanced by outward pressure from fusion energy (2). (c) becomes a red supergiant (1); explodes as a supernova (1); leaves a neutron star or black hole (1). (8)

13 (a) light from distant galaxies is shifted to longer/red wavelengths (1); because they are moving away from us (1). (b) red-shift; cosmic microwave background radiation (2). (4)

14 (a) scalar has magnitude only (1); vector has magnitude and direction (1) — e.g. scalar: mass/speed; vector: velocity/force (accept correct examples within the marks). (b) the extension of a spring is directly proportional to the force applied (1), up to the limit of proportionality (1). (c) k = F ÷ e = 10 ÷ 0.05 = 200 N/m (1 method, 1 answer). (d) as the object falls, air resistance increases with speed (1); until air resistance equals weight (1); resultant force is zero, so it falls at a constant maximum speed (1). (e) elastic potential energy (1). (10)

15 (a) transverse: oscillations perpendicular to the direction of energy transfer (e.g. light/water) (1+1); longitudinal: oscillations parallel to energy transfer (e.g. sound) (1). (b) radio, microwave, infrared, visible, ultraviolet, X-ray, gamma (2 — full/ordered list; 1 if minor error). (c) use: e.g. security marking / sun tanning / sterilising (1); danger: damages skin cells / can cause skin cancer / eye damage (1). (d) λ = v ÷ f = 320 ÷ 80 = 4 m (1 method, 1 answer). (e) it slows down (1). (10)

16 — Levels (6): Indicative: step-up transformers increase the voltage for transmission; for a given power, higher voltage means lower current; energy loss as heat in cables depends on current², so lower current = less wasted energy; step-down transformers reduce the voltage for safe use; transformers require a.c.

• L3 (5–6): Links high voltage → low current → less heat loss, and correctly uses step-up/step-down transformers.
• L2 (3–4): Some of the chain or the role of transformers.
• L1 (1–2): Simple statements.

17 — Levels (6): Indicative: a current-carrying conductor in a magnetic field experiences a force because the wire's field interacts with the magnet's field. The force is greatest when the wire is at 90° to the field and zero when parallel. The direction is reversed by reversing the current or the field (Fleming's left-hand rule). The size increases with a larger current or stronger field (F = BIL). Used in electric motors / loudspeakers.

• L3 (5–6): Explains the effect, how size and direction change, and names a device.
• L2 (3–4): Some explanation with one or two factors.
• L1 (1–2): Simple statements.

18 — Levels (6): Indicative: stopping distance = thinking distance + braking distance. Thinking distance (distance travelled during reaction time) increases with speed, tiredness, alcohol/drugs and distractions. Braking distance (distance while braking) increases with higher speed, worn brakes/tyres, wet or icy roads (less friction). During braking, the car's kinetic energy is transferred to thermal energy in the brakes, which heat up.

• L3 (5–6): Defines both parts, gives factors for each, and the brake energy transfer.
• L2 (3–4): Some factors and/or the energy transfer.
• L1 (1–2): Simple statements.

19 — Levels (6): Indicative: gravity pulls together a nebula (dust and gas) to form a protostar that heats up; fusion of hydrogen begins → main sequence star (stable: gravity balanced by outward pressure from fusion). When hydrogen runs low it expands to a red supergiant; it then explodes as a supernova; the remnant core forms a neutron star, or a black hole if massive enough. The supernova scatters elements into space.

• L3 (5–6): Correct, ordered life cycle through to neutron star/black hole.
• L2 (3–4): Several correct stages.
• L1 (1–2): Simple statements.

20 — Levels (6): Indicative: light from distant galaxies is shifted towards the red (longer wavelength) end of the spectrum; more distant galaxies show greater red-shift, showing the universe is expanding (galaxies moving away). Tracing this back suggests everything began from a tiny, hot, dense point (the Big Bang). The cosmic microwave background radiation is low-level radiation from all directions, predicted by and explained only by the Big Bang theory.

• L3 (5–6): Red-shift interpreted as expansion and CMB linked to the Big Bang.
• L2 (3–4): Some of the red-shift or CMB evidence.
• L1 (1–2): Simple statements.

21 — Levels (4): Indicative: sound waves make a diaphragm (and an attached coil) vibrate; the coil moves within a magnetic field; this induces a changing potential difference/current in the coil (the generator effect); the electrical signal varies with the same frequency as the sound.

• L2 (3–4): Links vibration of the coil in a field to an induced (changing) signal.
• L1 (1–2): Simple statements.

Sample Answers with Examiner Commentary

Question 16 — Sample Answers

Grade 9 answer "At the power station a step-up transformer increases the potential difference to a very high value for transmission. For a fixed amount of power, P = VI, so increasing the voltage means a much lower current flows in the cables. The energy wasted as heat in the cables depends on the current squared, so reducing the current greatly reduces the energy lost, making transmission efficient. Near homes and businesses, step-down transformers reduce the voltage again to a safe value (around 230 V). Transformers only work with alternating current, which is why the mains supply is a.c." Mark: 6/6. Examiner commentary: The full efficiency chain (high voltage → low current → less heat loss) is explained, with the correct role of both transformer types and the a.c. requirement. Top band.

Grade 6 answer "Step-up transformers make the voltage high for the wires and step-down transformers lower it for houses. High voltage means less energy is wasted as heat." Mark: 4/6. Examiner commentary: Correct roles of the transformers and the conclusion, but it does not explain that high voltage allows a lower current, which is why less heat is lost. That link is needed for the top band.

Question 11(c) — Sample Answers

Grade 9 answer "Vp/Vs = Np/Ns, so 230/Vs = 100/500. Rearranging, Vs = 230 × (500/100) = 230 × 5 = 1150 V." Mark: 3/3. Examiner commentary: Correct equation, substitution and answer with the unit.

Grade 6 answer "It's a step-up transformer so the voltage goes up. 230 × 5 = 1150 V." Mark: 2/3. Examiner commentary: Correct final answer and recognition that it steps up, but the transformer equation is not shown, losing the method mark for setting up the ratio.