Mark Scheme

Section A — Structured Questions (48 marks)

Question 1

(a) Define acceleration (2 marks)

• Acceleration is the rate of change of velocity [1]
• (Or: change in velocity per unit time) [1]

Accept: "change in velocity divided by time taken"
Reject: "change in speed" without reference to velocity

(b) Calculate average acceleration (3 marks)

• Use of v² = u² + 2as or listing v = 2.4 m/s, u = 0, s = 1.2 m [1]
• Correct substitution: (2.4)² = 0² + 2 × a × 1.2 [1]
• a = 2.4 m/s² [1]

Accept: use of v = u + at combined with s = ½(u + v)t to find a
Award [2] for correct answer with minimal working

(c) Effect on acceleration (2 marks)

• Acceleration increases [1]
• The component of weight down the slope increases / resultant force down slope increases [1]

Accept: "steeper slope means greater force"
Reject: "trolley goes faster" without reference to rate of change

(d) Calculate resultant force (2 marks)

• F = ma = 0.80 × 2.4 [1]
• F = 1.92 N (accept 1.9 N) [1]

(e) Suggest why resultant force is less (1 mark)

• Friction / air resistance opposes motion [1]

Accept: "energy is lost to friction/heat"
Accept: "resistive forces act up the slope"

Question 2

(a)(i) Loss in GPE per second (3 marks)

• Use of ΔPE = mgΔh [1]
• Correct substitution: ΔPE = 1500 × 10 × 85 [1]
• ΔPE = 1 275 000 J (or 1.275 MJ or 1.28 MJ) [1]

Accept: 1.3 MJ

(a)(ii) What happens to GPE (1 mark)

• Converted to kinetic energy / electrical energy / heat / sound [1]

Accept: any one sensible energy transfer

(b) Calculate efficiency (3 marks)

• Efficiency = (useful output / total input) × 100% [1]
• Correct substitution: (9.6 × 10⁶ / 1.275 × 10⁶) × 100% or (9600000/1275000) × 100 [1]
• Efficiency = 75.3% (accept 75% to 76%) [1]

Award [2] for answer 0.753 without percentage

(c)(i) Explain transmission at high voltage (2 marks)

• High voltage means low(er) current (for the same power) [1]
• Low(er) current reduces energy loss / heat loss / power loss in cables / transmission lines [1]

Reject: "high voltage reduces resistance" - resistance is a property of the conductor
Accept: reference to P = I²R to explain heating effect

(c)(ii) Calculate current in primary (3 marks)

• Use of P = VI [1]
• Correct substitution: 9.6 × 10⁶ = I × 25 × 10³ or 9 600 000 = I × 25 000 [1]
• I = 384 A (accept 380–390 A) [1]

Accept: working that accounts for 98% efficiency if clearly shown

Question 3

(a) Ray diagram (3 marks)

• Ray 1: drawn from top of object parallel to axis, refracting through far focal point [1]
• Ray 2: drawn from top of object through centre of lens, continuing straight [1]
• Image correctly positioned where rays meet, inverted, between F and 2F on opposite side [1]

Deduct [1] if rays not drawn with ruler / are freehand curves
Deduct [1] if arrowheads missing or incorrectly placed

(b) Three characteristics (3 marks)

• Real [1]
• Inverted / upside down [1]
• Diminished / smaller than object [1]

Accept: "same way up as object" scores [0] for that point
All three required for full marks

(c)(i) Calculate image distance (3 marks)

• Use of 1/f = 1/u + 1/v [1]
• Correct substitution: 1/8.0 = 1/20 + 1/v [1]
• v = 13.3 cm (accept 13 cm to 13.5 cm) [1]

Accept: use of similar triangles method with full working

(c)(ii) Calculate magnification (2 marks)

• Correct substitution: magnification = 13.3 / 20 [1]
• Magnification = 0.67 (accept 0.65 to 0.70) [1]

Accept: magnification stated as ×0.67 or 67%
Award [1] only if answer from (c)(i) is used consistently

(d) Describe image when object at 6.0 cm (2 marks)

• Virtual / cannot be projected on screen [1]
• Upright / magnified / same side of lens as object [1]

Accept any two correct characteristics
Reject: "real" or "inverted"

Question 4

(a) Explain random process (2 marks)

• Cannot predict when a particular nucleus will decay / which nucleus will decay next [1]
• (But) the rate/probability of decay is constant / not affected by external conditions [1]

Accept: "decay is spontaneous"
Reject: "decay is unpredictable" alone without further explanation

(b)(i) Define half-life (2 marks)

• The time taken for half the (radioactive) nuclei to decay [1]
• Or: the time taken for the activity/count rate to fall to half its original value [1]

Either definition scores full [2] marks
Reject: "half the atoms disappear" without reference to decay

(b)(ii) Calculate activity after 15 hours (3 marks)

• Recognition that 15 hours = 3 half-lives [1]
• Correct process: 1200 → 600 → 300 → 150 or 1200 × (½)³ [1]
• Activity = 150 Bq [1]

Award [2] for correct answer with minimal working

(c)(i) Nature of beta particle (2 marks)

• (Fast-moving) electron [1]
• Emitted from the nucleus / formed when a neutron changes to a proton [1]

Accept: "high-energy electron"
Accept: "negative charge" for second mark if first mark awarded

(c)(ii) Investigation of range safely (3 marks)

• Use Geiger counter / radiation detector at varying distances from source [1]
• Measure count rate at each distance / until count rate falls to background level [1]
• Safety: keep source in lead container when not in use / use handling tongs / keep source away from body / minimize exposure time / no eating or drinking [1]

Any three valid points from experimental method and safety
Must have at least one safety point for full marks

Question 5

(a) State equation (1 mark)

• P = E/t or E = Pt or Power = energy/time [1]

Accept: word equation clearly stated

(b) Calculate energy supplied (2 marks)

• E = 120 × 240 [1]
• E = 28 800 J (accept 28.8 kJ or 29 kJ) [1]

(c) Calculate specific heat capacity (4 marks)

• Temperature rise = 52 – 20 = 32 °C [1]
• Use of E = mcΔθ or c = E/(mΔθ) [1]
• Correct substitution: 28 800 = 2.0 × c × 32 or c = 28 800/(2.0 × 32) [1]
• c = 450 J/(kg °C) [1]

Accept: 440–460 J/(kg °C) accounting for rounding
Award max [3] if answer from (b) used incorrectly but method correct

(d) Reasons for difference (2 marks)

Any two from:

• Heat lost to surroundings / not all energy goes into copper block [1]
• Heat absorbed by heater / thermometer / container [1]
• Inaccurate temperature readings / thermometer not calibrated [1]
• Energy lost by evaporation (if any liquid used) [1]

Max [2] marks
Must be two distinct reasons

Question 6

(a) Combined resistance of R₂ and R₃ (3 marks)

• Use of 1/R = 1/R₂ + 1/R₃ or R = (R₂ × R₃)/(R₂ + R₃) [1]
• Correct substitution: 1/R = 1/6.0 + 1/12 or R = (6.0 × 12)/(6.0 + 12) [1]
• R = 4.0 Ω [1]

Accept: alternative valid method with correct answer

(b) Total resistance (1 mark)

• R_total = 4.0 + 4.0 = 8.0 Ω [1]

Award mark if follows from answer to part (a)

(c) Current through R₁ (2 marks)

• Use of V = IR or I = V/R [1]
• I = 12/8.0 = 1.5 A [1]

Award mark if follows from answer to part (b)

(d) Potential difference across R₂ (3 marks)

• V across parallel combination = V_total – V across R₁ [1]
• V_R₁ = 1.5 × 4.0 = 6.0 V or V across parallel = 12 – 6.0 [1]
• V across R₂ = 6.0 V [1]

Accept: alternative route: current through R₂ = 1.0 A, then V = IR = 1.0 × 6.0 = 6.0 V
Award marks if method is consistent with earlier answers

(e) Effect of higher internal resistance (2 marks)

• Current decreases / becomes smaller [1]
• (Because) more voltage is dropped across / lost in the internal resistance / less p.d. available for external circuit [1]

Accept: "total resistance increases so current decreases"
Reject: "battery runs down faster" without reference to circuit current

Section B — Extended Response (32 marks)

Question 7

(a) Describe nuclear fission (6 marks)

Level 3 (5–6 marks):

• Comprehensive description of fission process
• Clear explanation of role of neutrons as both trigger and product
• Chain reaction explained with reference to sustainability
• Correct use of terminology throughout

Level 2 (3–4 marks):

• Basic description of fission process
• Role of neutrons mentioned
• Some reference to chain reaction
• Most terminology correct

Level 1 (1–2 marks):

• Limited description
• May mention nucleus splitting
• Terminology imprecise or incorrect

Indicative content:

• Large/heavy nucleus (e.g. uranium-235/plutonium-239) absorbs a neutron [1]
• Nucleus becomes unstable and splits into two (or more) smaller nuclei/daughter nuclei [1]
• Energy is released (as kinetic energy of products/heat) [1]
• Two or three neutrons are released in the fission [1]
• These neutrons can go on to cause further fission events/reactions [1]
• Chain reaction: self-sustaining if each fission causes (on average) at least one more fission [1]
• Control rods absorb neutrons to control reaction rate [1]
• Moderator slows neutrons to increase probability of fission [1]

Award up to 6 marks for clear, well-structured response covering main points

(b) Discuss advantages and disadvantages (10 marks)

Level 4 (9–10 marks): A comprehensive and balanced evaluation that:

• Addresses all bullet points in detail
• Provides well-developed arguments for and against
• Makes explicit comparisons with fossil fuels throughout
• Uses scientific terminology accurately
• Reaches a reasoned conclusion based on evidence presented
• Demonstrates clear, logical structure

Level 3 (6–8 marks): A sound discussion that:

• Addresses most bullet points with some detail
• Provides arguments for and against with some development
• Makes some comparisons with fossil fuels
• Uses scientific terminology mainly correctly
• May reach a conclusion
• Generally well-structured

Level 2 (3–5 marks): A basic discussion that:

• Addresses some bullet points
• Provides simple arguments for and/or against
• Limited comparison with fossil fuels
• Some correct scientific terminology
• May be imbalanced (only advantages or only disadvantages)
• Limited structure

Level 1 (1–2 marks): A limited response that:

• Mentions one or two points
• Little or no development
• May be entirely one-sided
• Terminology imprecise
• Lacks structure

Indicative content:

Advantages:

• No greenhouse gas emissions during operation / reduces contribution to climate change
• Very large amounts of energy from small amounts of fuel
• Fuel (uranium) is relatively abundant / will last longer than fossil fuels
• Reliable baseload power / not weather-dependent
• Energy security / reduces dependence on imported fossil fuels
• Low fuel costs per unit of energy produced

Disadvantages:

• Radioactive waste remains dangerous for thousands/millions of years
• No satisfactory long-term waste disposal solution
• Risk of accidents with serious consequences (Chernobyl, Fukushima)
• High construction and decommissioning costs
• Thermal pollution of water bodies used for cooling
• Target for terrorism
• Public concerns/opposition
• Long construction times
• Risk of nuclear weapons proliferation

Fossil fuel comparisons:

• Fossil fuels: produce CO₂ (greenhouse gas) vs nuclear: no CO₂ during operation
• Fossil fuels: produce acid rain pollutants vs nuclear: no chemical pollution
• Fossil fuels: waste is not radioactive vs nuclear: radioactive waste problem
• Fossil fuels: established infrastructure vs nuclear: requires specialist facilities
• Both: non-renewable (though nuclear fuel lasts longer)

Award marks holistically based on level descriptors

Question 8

(a) Time for radio signal (3 marks)

• Use of speed = distance/time or time = distance/speed [1]
• Correct substitution: t = 6.0 × 10¹¹ / 3.0 × 10⁸ [1]
• t = 2000 s = 33.3 minutes (accept 33 min) or 2.0 × 10³ s with conversion shown [1]

Award [2] for answer in seconds only
Accept: 0.56 hours if clearly shown

(b) Maximum electrical power (4 marks)

• Calculate total solar power received: Power = intensity × area [1]
• Correct substitution: P = 15 × 25 [1]
• P = 375 W [1]
• Apply efficiency: P_electrical = 0.20 × 375 = 75 W (accept 75 W clearly obtained) [1]

Award [3] if final calculation not clearly shown but answer is correct
Accept: combined calculation 15 × 25 × 0.20 = 75 W for full marks if working shown

(c) Evaluate whether probe can operate (9 marks)

Level 3 (7–9 marks): A complete evaluation that:

• Correctly calculates energy required during eclipse
• Correctly compares with stored energy
• Clearly states whether probe can operate with justification
• Includes consideration of time period
• All working shown with correct units
• Reaches a clear, justified conclusion

Level 2 (4–6 marks): A partial evaluation that:

• Attempts to calculate energy required
• Makes some comparison with stored energy
• Some working shown
• May have minor errors in calculation or unit conversion
• Conclusion may be stated but not fully justified

Level 1 (1–3 marks): A limited attempt that:

• Shows some relevant calculation
• Limited or no comparison
• Significant errors in method or calculation
• Conclusion missing or unjustified

Model answer content:

• Time of eclipse in seconds: 8.0 hours = 8.0 × 60 × 60 = 28 800 s [1]
• Energy required: E = P × t [1]
• E = 65 × 28 800 [1]
• E = 1 872 000 J = 1.872 MJ [1]
• Comparison: stored energy = 4.5 MJ [1]
• Recognition that 4.5 MJ > 1.872 MJ [1]
• Clear statement: Yes, probe can operate throughout eclipse [1]
• Justification: stored energy exceeds required energy [1]
• Additional: 2.628 MJ remains / sufficient reserve [1]

Alternative approaches:

• Calculate how long batteries would last: t = E/P = 4.5 × 10⁶ / 65 = 69 230 s = 19.2 hours
• Compare with 8.0 hours eclipse
• Conclude batteries last longer than eclipse

Award marks based on level descriptors for quality of evaluation
Maximum [9] marks for complete, well-structured evaluation with justified conclusion

Sample Answers with Examiner Commentary

Question 7(b) — Sample Answers

Grade A (high distinction) answer*

Nuclear fission has several significant advantages over fossil fuels for electricity generation. Most importantly, nuclear power stations produce no carbon dioxide during operation, which means they do not contribute to climate change or global warming, whereas burning fossil fuels releases large quantities of CO₂ which is a major greenhouse gas. Nuclear fuel (uranium) also produces enormous amounts of energy from very small masses - one kilogram of uranium can produce as much energy as several million kilograms of coal. This means fuel costs per unit of energy are very low and uranium resources will last much longer than fossil fuel reserves. Nuclear power also provides reliable baseload electricity that is not weather-dependent, unlike renewables, and reduces a country's dependence on imported fossil fuels, improving energy security.

However, nuclear power has serious disadvantages. The radioactive waste produced remains hazardous for thousands or even millions of years, and there is currently no satisfactory long-term disposal solution - waste must be stored carefully and monitored indefinitely, which is very expensive. Although modern nuclear plants are designed with multiple safety systems, accidents can have catastrophic consequences, as seen at Chernobyl and Fukushima, releasing radioactivity over wide areas and rendering land uninhabitable. The construction costs of nuclear power stations are extremely high (billions of pounds) and decommissioning old plants is also very costly and time-consuming. Nuclear plants also cause thermal pollution as they use large quantities of cooling water from rivers or seas, which is returned at higher temperatures, affecting aquatic ecosystems. There are also concerns about nuclear materials being targeted by terrorists or being diverted to weapons programs.

Fossil fuel plants also have environmental problems - they produce sulfur dioxide and nitrogen oxides which cause acid rain, and particulates which damage human health - but these emissions can be controlled with scrubbers. Their waste products are not radioactive, which is much easier to manage than nuclear waste. However, the CO₂ problem from fossil fuels is arguably more urgent as climate change affects the entire planet.

Overall, whether nuclear power is preferable to fossil fuels depends on how different factors are weighted. In terms of climate change, nuclear is clearly better as it is effectively carbon-free. For long-term sustainability, nuclear is also better as uranium will last longer than fossil fuels. However, the waste disposal problem and accident risks are unique to nuclear power and represent serious long-term challenges. Many scientists argue that nuclear power must be part of the energy mix if we are to reduce CO₂ emissions quickly enough to prevent dangerous climate change, but this must be balanced against the genuine risks and costs involved.

Mark: 10/10

Examiner commentary: This is an exemplary response demonstrating all the characteristics of high-level evaluation. The student addresses all four bullet points comprehensively with well-developed arguments. Comparisons with fossil fuels are explicit and integrated throughout rather than treated separately. Scientific terminology is used precisely (greenhouse gas, baseload, radioactive isotopes, thermal pollution). The structure is logical, moving from advantages to disadvantages then to an evaluative conclusion. The conclusion weighs competing factors and acknowledges that the answer depends on priorities, which demonstrates sophisticated thinking. The student references specific evidence (Chernobyl, Fukushima) and quantifies claims where possible (millions of years, billions of pounds). This fully satisfies the Level 4 descriptor.

Grade C (pass) answer

Nuclear power has advantages and disadvantages compared to fossil fuels.

Advantages: Nuclear power doesn't produce carbon dioxide or other greenhouse gases when it's running, so it doesn't cause global warming like fossil fuels do. Uranium is quite abundant and a small amount produces lots of energy. Nuclear power stations can produce electricity all the time, not like wind or solar which only work sometimes. It means countries don't have to import so much oil or gas from other countries.

Disadvantages: The main problem is radioactive waste which is very dangerous for thousands of years and we don't really know how to dispose of it safely. If there's an accident, lots of radioactivity can escape and contaminate a large area, like at Chernobyl. Nuclear power stations are very expensive to build. There's also the risk that the materials could be used to make nuclear weapons.

Fossil fuels also cause pollution - they make acid rain and release CO₂ which causes climate change. But their waste isn't radioactive. Fossil fuels will eventually run out but there's still quite a lot left.

In conclusion, nuclear power is better for the environment in terms of climate change because it doesn't release CO₂. But the waste problem and danger of accidents are serious issues. It's probably a good idea to use some nuclear power along with other types of energy.

Mark: 6/10

Examiner commentary: This response demonstrates sound understanding and achieves Level 3. The student addresses all four bullet points (environmental, fuel supply, safety/waste, evaluation) but with less depth than the A* answer. Advantages and disadvantages are clearly stated with some development. However, the fossil fuel comparisons are somewhat superficial - mentioned mainly in a separate paragraph rather than integrated throughout. The conclusion attempts evaluation but is relatively brief and doesn't weigh competing factors as thoroughly. Scientific terminology is mostly correct but less sophisticated ("lots of energy," "very dangerous" rather than quantifying). To reach Level 4, this student needed to develop arguments more fully, make more explicit comparisons throughout, and provide a more nuanced conclusion. The structure is adequate but lacks the sophistication of the top-band response.

Grade E (near miss) answer

Nuclear power is good because it doesn't pollute the air like coal and oil do. It makes lots of electricity from a small amount of fuel. The fuel will last a long time.

But nuclear power is very dangerous. If something goes wrong the whole power station can explode and kill lots of people. The waste is radioactive and will kill you if you go near it. It has to be buried underground forever.

Fossil fuels cause global warming because of CO₂. They also pollute the air. But at least they don't explode like nuclear plants.

I think fossil fuels are safer because there's no radiation. But nuclear is better for global warming.

Mark: 3/10

Examiner commentary: This response achieves low Level 2. The student demonstrates some basic knowledge - recognizing that nuclear doesn't produce air pollution, that radioactive waste is hazardous, and that fossil fuels produce CO₂. However, there are significant weaknesses that prevent higher marks. The response contains a major misconception: nuclear power stations do not "explode" (this conflates nuclear reactors with nuclear bombs; accidents involve meltdown and radiation release, not explosion). The discussion is superficial with minimal development of any point. Key terminology is vague ("pollute the air," "lots of electricity") without scientific precision. The structure is very basic with simple lists rather than developed arguments. The fuel supply and energy security points are barely addressed. The conclusion is simplistic and doesn't constitute real evaluation. To improve, the student needs to: correct the misconception about explosions; develop each point with explanation; use correct terminology (CO₂ as greenhouse gas, half-life of waste, etc.); provide a more structured comparison; and attempt genuine evaluation weighing different factors.

Question 8(c) — Sample Answers

Grade A (high distinction) answer*

First, I need to calculate the total energy required by the probe during the 8.0 hour eclipse.

Converting time to seconds: 8.0 hours = 8.0 × 60 × 60 = 28,800 s

The probe requires 65 W of power, which means it uses 65 J every second.

Energy required = Power × time E = P × t = 65 W × 28,800 s E = 1,872,000 J

Converting to MJ for easier comparison: E = 1.872 MJ

The batteries store a total of 4.5 MJ of energy.

Comparing the two values: Energy stored = 4.5 MJ Energy required = 1.872 MJ

Since 4.5 MJ > 1.872 MJ, the stored energy exceeds the required energy.

Therefore, yes, the probe can continue to operate throughout the eclipse period.

The batteries contain sufficient energy to power the probe for the entire duration of the eclipse. In fact, there would be surplus energy remaining:

Surplus energy = 4.5 - 1.872 = 2.628 MJ

This reserve would allow the probe to continue operating for additional time after the eclipse ends, or could be used if the eclipse lasted longer than expected, providing a safety margin.

Alternatively, I can check how long the batteries would last:

Time batteries last = Energy stored / Power required t = 4.5 × 10⁶ J / 65 W t = 69,230 s = 19.2 hours

Since the batteries can power the probe for 19.2 hours, and the eclipse only lasts 8.0 hours, this confirms the probe can definitely operate throughout.

Mark: 9/9

Examiner commentary: This is an exemplary extended calculation and evaluation. The student demonstrates Level 3 characteristics: systematic working through the problem with all steps shown clearly; correct conversion of units (hours to seconds, J to MJ); accurate calculations with proper significant figures; explicit comparison between stored and required energy; a clear conclusion directly answering the question; and quantification of the surplus energy showing depth of analysis. The alternative verification method (calculating battery lifetime) shows mathematical confidence and provides additional evidence for the conclusion. The mention of a "safety margin" demonstrates scientific thinking beyond the basic calculation. All working is clearly laid out with appropriate units throughout. This fully exemplifies the Level 3 descriptor for 7-9 marks and achieves full marks.

Grade C (pass) answer

The probe needs 65 W of power.

The eclipse lasts 8.0 hours = 8 × 60 × 60 = 28,800 seconds

Energy needed = 65 × 28,800 = 1,872,000 J

This is 1.872 MJ.

The batteries have 4.5 MJ stored.

4.5 is bigger than 1.872, so yes the probe can operate during the eclipse because there's enough energy in the batteries.

The probe will have some energy left over: 4.5 - 1.872 = 2.628 MJ left

Mark: 5/9

Examiner commentary: This response achieves Level 2. The student performs the essential calculations correctly: converts time to seconds, calculates energy required, converts to MJ, and makes the comparison. A clear conclusion is stated. However, the presentation lacks the sophistication of the A* answer - there's minimal explanation of what each calculation represents (no equation labels like "E = Pt"), and the reasoning is less explicitly justified. The statement "4.5 is bigger than 1.872" is correct but lacks formal comparison ("exceeds" / "greater than required energy"). The student calculates surplus energy but doesn't interpret its significance (safety margin, additional operating time). To reach Level 3, this answer needed: clearer labeling of equations and steps; more explicit justification of the conclusion ("stored energy exceeds required energy by 2.628 MJ, therefore..."); and perhaps verification through an alternative method. The mathematics is sound but the evaluation component is underdeveloped.

Grade E (near miss) answer

Eclipse time = 8 hours

Power = 65 W

Energy = 65 × 8 = 520 J

Batteries have 4.5 MJ = 4,500,000 J

4,500,000 is much more than 520, so yes the probe can work.

Mark: 2/9

Examiner commentary: This response achieves only low Level 1. The student recognizes that a comparison between stored and required energy is needed, which shows some understanding of the task. However, there is a critical error: multiplying power (65 W) by time in hours (8) directly, which gives an answer in the wrong units (the unit would be W·h, not J, and the numerical value is far too small). The student has failed to convert hours to seconds before applying E = Pt. This is a common misconception at this level - not recognizing that standard SI units must be used in equations. Consequently, the comparison is invalid even though the conclusion happens to be correct. The working shown is minimal. To improve, the student must: understand that time must be in seconds when power is in watts; show the conversion explicitly (8 × 60 × 60); perform the correct calculation E = 65 × 28,800; then make a valid comparison. Additionally, the evaluation lacks any development - there's no discussion of surplus energy, no verification, and no justification beyond "much more than." This answer demonstrates the typical errors of a student who understands the basic concept (compare energies) but cannot execute the calculation correctly or provide adequate evaluation.