Mark Scheme

Section A — Structured Questions

QUESTION 1

(a)

• Average time = (2.2 + 2.0 + 2.1) ÷ 3 = 2.1 s
• [1 mark] for correct answer with or without working

(b)

• Average speed = distance ÷ time
• = 2.0 ÷ 2.1
• = 0.95 m s⁻¹ (or 0.952 m s⁻¹)
• [1 mark] for correct formula or correct substitution
• [1 mark] for correct answer with unit
• Accept range 0.90–0.96 m s⁻¹

(c) (i)

• The trolley moves faster as it goes down the slope / speed increases / velocity increases with time
• [1 mark] for any valid observation indicating increasing speed
• Reject: "it speeds up" without further qualification

(ii)

• There is a component of weight / gravitational force acting down the slope
• This force is greater than friction / air resistance / resistive forces
• Therefore there is a resultant / net / unbalanced force down the slope (causing acceleration)
• [1 mark] for identifying driving force down the slope
• [1 mark] for explaining resultant/unbalanced force or stating driving force exceeds resistive forces
• Accept: "gravitational potential energy converts to kinetic energy" for second mark

(d)

• To improve reliability / accuracy of results / reduce effect of random errors / identify anomalies / calculate average
• [1 mark] for any valid reason
• Reject: "to make sure it is correct" without further detail

QUESTION 2

(a) (i)

• To provide a low-resistance path to earth / ground for current (in case of fault)
• To prevent electric shock / protect the user / prevent casing becoming live
• [1 mark] for either point
• Accept: "safety" with appropriate elaboration

(ii)

• If the fuse were in the neutral wire, the appliance would remain connected to the live wire even when the fuse blows
• This means the appliance casing could still be at high voltage / live / dangerous
• [1 mark] for stating appliance remains connected to live
• [1 mark] for explaining continued danger / risk of shock

(b)

• P = VI or I = P ÷ V
• I = 2000 ÷ 230
• = 8.7 A (or 8.70 A or 8.695... A)
• [1 mark] for correct formula or substitution
• [1 mark] for correct answer with unit
• Accept range 8.6–8.8 A

(c)

• 10 A fuse
• Because the operating current is 8.7 A and the fuse must be rated slightly above this / the 10 A fuse is the next size up / the 5 A fuse would blow during normal operation / the 13 A fuse would allow too much current before blowing
• [1 mark] for 10 A
• [1 mark] for correct reasoning

(d)

• E = mcΔθ or Q = mcΔT
• = 1.5 × 4200 × (100 – 28) or = 1.5 × 4200 × 72
• = 453 600 J or 454 kJ or 4.54 × 10⁵ J
• [1 mark] for correct formula
• [1 mark] for correct substitution including temperature change
• [1 mark] for correct answer with unit
• Accept range 450 000–455 000 J or equivalent in kJ

QUESTION 3

(a) (i)

• The (complete) range / family of electromagnetic waves / radiation
• Arranged in order of frequency / wavelength / energy
• [1 mark] for identifying it as a range/family of waves
• [1 mark] for stating order of arrangement
• Accept: both marks for "the complete range of electromagnetic waves from radio waves to gamma rays in order of frequency/wavelength"

(ii)

• Any TWO from: ultraviolet (UV) / X-rays / gamma rays
• [1 mark] for each correct region (maximum 2 marks)

(b) (i)

• Electrons absorb energy and move to higher energy levels / become excited
• When electrons fall back to lower energy levels, they emit energy as photons / light
• [1 mark] for electrons moving to higher energy levels
• [1 mark] for electrons falling back and emitting photons/light
• Accept: "electrons drop down" for second mark

(ii)

• Energy levels in atoms are discrete / quantized / fixed / specific
• Only certain / specific energy transitions are possible
• Therefore only certain / specific frequencies / wavelengths / colours are emitted
• [1 mark] for discrete/quantized energy levels
• [1 mark] for linking this to specific frequencies/wavelengths emitted
• Reject: "because hydrogen has separated energy levels" without explanation of why this produces lines

(c)

• c = fλ or f = c ÷ λ
• f = (3.00 × 10⁸) ÷ (6.56 × 10⁻⁷)
• = 4.57 × 10¹⁴ Hz (or 4.6 × 10¹⁴ Hz)
• [1 mark] for correct formula and substitution
• [1 mark] for correct answer with unit in standard form
• Accept range 4.5–4.6 × 10¹⁴ Hz

QUESTION 4

(a)

• A reflected sound / sound reflected from a surface / sound that bounces back
• [1 mark] for correct definition
• Must mention reflection or bouncing back

(b)

• Total distance = speed × time = 340 × 4.0 = 1360 m
• Distance to mountain = 1360 ÷ 2 = 680 m
• (or direct calculation: distance = (340 × 4.0) ÷ 2 = 680 m)
• [1 mark] for correct formula (distance = speed × time)
• [1 mark] for recognizing need to divide by 2 / that sound travels to mountain and back
• [1 mark] for correct answer with unit
• Accept range 675–685 m

(c)

• Any TWO from:
  • Sound energy is absorbed by the mountain / surface
  • Sound energy spreads out / disperses over distance
  • Sound energy is absorbed by the air
  • Sound energy is scattered by obstacles / irregularities in the surface
• [1 mark] for each valid reason (maximum 2 marks)
• Accept: "energy is lost" only if mechanism is specified

(d) (i)

• Doppler effect
• [1 mark] for correct name
• Accept: "Doppler shift"

(ii)

• As the car approaches, the frequency appears higher (than the actual frequency) / pitch is higher
• As the car moves away, the frequency appears lower (than the actual frequency) / pitch is lower
• [1 mark] for correct description as car approaches
• [1 mark] for correct description as car moves away
• Accept: "wavelength decreases" and "wavelength increases" as equivalents

Section B — Extended Response

QUESTION 5

(a) Marks awarded for description of nuclear fission process (8 marks)

Mark allocation:

• [1 mark] A neutron strikes/collides with a uranium-235 nucleus
• [1 mark] The nucleus splits / undergoes fission into two smaller nuclei / daughter nuclei / fragments
• [1 mark] Additional neutrons are released (typically 2 or 3)
• [1 mark] Energy is released (as kinetic energy of products / heat)
• [1 mark] These neutrons can strike other uranium nuclei
• [1 mark] Creating a chain reaction / self-sustaining reaction
• [1 mark] The kinetic energy heats water to produce steam
• [1 mark] Steam drives turbines connected to generators that produce electricity
• Maximum 8 marks
• Accept equivalent descriptions at each stage
• Accept diagrams with labels if clear, but written explanation must also be present for full marks

(b) Evaluation of nuclear vs geothermal energy (16 marks)

Level 4 (13–16 marks): A comprehensive and balanced evaluation that:

• Discusses environmental impacts of both methods with specific detail (e.g., radioactive waste vs minimal environmental impact; both have low operational emissions)
• Analyzes economic factors including initial costs, running costs, and long-term economics
• Addresses safety considerations for both technologies with reference to risks
• Explicitly considers Caribbean context (e.g., geothermal availability in volcanic islands like Saint Lucia and Dominica; lack of uranium resources; vulnerability to hurricanes; small grid sizes)
• Makes a clear, well-justified recommendation based on the evidence presented
• Uses appropriate scientific terminology throughout
• Presents a logical, well-structured argument with developed points

Level 3 (9–12 marks): A sound evaluation that:

• Discusses environmental and economic factors for both methods
• Addresses safety considerations
• Makes some reference to Caribbean context
• Makes a recommendation with some justification
• Uses appropriate terminology generally correctly
• Shows clear understanding but lacks the depth and development of Level 4

Level 2 (5–8 marks): A basic evaluation that:

• Identifies some advantages and disadvantages of each method
• Limited discussion of Caribbean context
• May make a recommendation but with weak justification
• Some correct terminology but may contain errors
• Structure may be unclear or unbalanced

Level 1 (1–4 marks): A limited response that:

• Lists some simple points about one or both methods
• Little or no evaluation or comparison
• Minimal or no reference to Caribbean context
• Recommendation may be absent or unjustified
• Limited use of scientific terminology

0 marks: No creditworthy material

Indicative content (not prescriptive):

Environmental:

• Both have very low operational CO₂ emissions (advantage over fossil fuels)
• Nuclear produces long-lived radioactive waste requiring secure storage for thousands of years
• Geothermal has minimal waste products
• Both have relatively small land footprint compared to solar/wind

Economic:

• Nuclear has very high initial capital costs; geothermal moderate
• Nuclear has high energy density / output per unit fuel
• Caribbean countries generally small economies; nuclear may be too expensive
• Geothermal has lower running costs and shorter construction time
• No uranium in Caribbean; would need to import fuel for nuclear
• Geothermal resources available in volcanic islands

Safety:

• Nuclear has low probability but high-consequence risks (e.g., Fukushima, Chernobyl)
• Caribbean vulnerable to hurricanes, earthquakes, and tsunamis which could compromise nuclear safety
• Geothermal has very low risk profile
• Nuclear requires highly trained workforce; may be challenge in small Caribbean nations

Caribbean context:

• Several Eastern Caribbean islands (Dominica, Saint Lucia, Nevis) have geothermal potential
• Small electricity grids; large nuclear plant may be inappropriate scale
• No nuclear expertise or infrastructure in region
• Geothermal suits distributed, smaller-scale generation

Likely justified recommendation: Geothermal more appropriate for Caribbean because:

• Locally available resource in volcanic islands
• Appropriate scale for small island grids
• Lower capital cost
• Lower risk profile
• No fuel import dependency
• However, nuclear might be mentioned as theoretically possible for larger islands or regional cooperation schemes

Sample Answers with Examiner Commentary

Question 5(b) — Sample Answers

Grade I (Distinction) answer

When evaluating nuclear fission versus geothermal energy for Caribbean electricity generation, several key factors must be considered: environmental impact, economic viability, safety, and regional suitability.

From an environmental perspective, both methods have significant advantages over fossil fuels, as both produce very low CO₂ emissions during operation. However, nuclear fission creates long-lived radioactive waste that remains hazardous for thousands of years and requires secure geological storage facilities. In contrast, geothermal energy produces minimal waste—mostly dissolved minerals that can be re-injected into the reservoir. Both have relatively small land footprints, which is advantageous for small island states.

Economically, there are substantial differences. Nuclear power stations require enormous initial capital investment—typically billions of dollars—which may be prohibitive for small Caribbean economies like Saint Lucia or Dominica. While nuclear fuel (uranium-235) produces extremely high energy output per kilogram, the Caribbean has no uranium deposits and would be dependent on imports. Geothermal installations have moderate construction costs and use a local, renewable resource, eliminating fuel import costs. The running costs of geothermal are also lower, and construction times are shorter. For small island grids with electricity demands in the tens of megawatts, a large nuclear reactor would be inappropriate in scale, whereas geothermal plants can be built at scales suitable for island needs.

Safety considerations strongly favour geothermal energy in the Caribbean context. Although modern nuclear plants have low probability of accidents, when failures occur (such as Fukushima in 2011 or Chernobyl in 1986), the consequences are catastrophic. The Caribbean region is vulnerable to hurricanes, earthquakes, and tsunamis—all of which could compromise nuclear safety systems. The Fukushima disaster was triggered by a tsunami following an earthquake, demonstrating exactly the kind of risk Caribbean islands face. Geothermal installations have an excellent safety record with very low risk of catastrophic failure. Additionally, nuclear technology requires highly specialized technical expertise and regulatory infrastructure that small Caribbean nations would struggle to develop and maintain.

Regarding Caribbean suitability, several Eastern Caribbean islands—including Dominica, Saint Lucia, Nevis, and Montserrat—sit on volcanic arcs and possess significant geothermal resources. Dominica has actively explored geothermal development and aims to become the world's first climate-resilient nation partly through geothermal energy. These islands have the natural advantage of accessible geothermal reservoirs. In contrast, there is no nuclear infrastructure, expertise, or regulatory framework in the region.

In conclusion, geothermal energy is far more appropriate than nuclear fission for Caribbean countries like Saint Lucia or Dominica. The combination of locally available geothermal resources, appropriate scale for island grids, lower capital costs, minimal safety risks, elimination of fuel imports, and suitability for the hurricane- and earthquake-prone region makes geothermal the logical choice. While nuclear energy might theoretically be considered for a large regional cooperation project, the practical, economic, and safety barriers make it unsuitable for individual Caribbean nations. Geothermal represents a realistic, sustainable pathway to energy independence for volcanic Caribbean islands.

Mark: 16/16

Examiner commentary: This is an exemplary response demonstrating all the qualities expected at Level 4. The candidate provides a comprehensive, balanced evaluation with detailed discussion of environmental, economic, and safety factors. The Caribbean context is thoroughly integrated throughout, with specific reference to named countries, regional hazards (hurricanes, earthquakes, tsunamis), and real examples (Dominica's geothermal development, Fukushima disaster). The recommendation is clear, well-justified, and flows logically from the evidence presented. Scientific terminology is used accurately throughout, and the response is well-structured with developed paragraphs addressing each assessment criterion. This demonstrates the analytical thinking and application of knowledge expected of a Grade I candidate.

Grade III (Pass) answer

Nuclear fission and geothermal energy are both ways to generate electricity with low carbon emissions. Each has advantages and disadvantages.

Nuclear power produces a lot of energy from a small amount of fuel. One kilogram of uranium can produce much more energy than coal or oil. It also doesn't produce CO₂ when it's operating, which is good for the environment. However, nuclear power creates radioactive waste which is very dangerous and lasts for thousands of years. This waste has to be stored carefully. Nuclear power stations are also very expensive to build, costing billions of dollars. There is also the risk of accidents like Chernobyl or Fukushima, which can be devastating. Nuclear power needs highly trained workers and special safety systems.

Geothermal energy uses heat from inside the Earth to generate electricity. It is renewable because the heat keeps being produced. It also produces very low CO₂ emissions and doesn't create dangerous waste like nuclear does. The cost to build geothermal plants is less than nuclear, which is important for Caribbean countries that don't have large budgets. Geothermal is also safer because there's no risk of a nuclear accident.

For the Caribbean, geothermal energy is probably better. Some Caribbean islands like Dominica and Saint Lucia have volcanoes, so they have geothermal resources available. The Caribbean doesn't have any uranium, so they would have to import it for nuclear power. Caribbean islands are also hit by hurricanes, which could damage a nuclear power station. The islands are quite small, so a large nuclear power station might be too big for their needs. Geothermal plants can be smaller and built to the right size for the island.

In conclusion, I think geothermal energy is more appropriate for Caribbean countries. It is cheaper, safer, uses local resources, and is the right size for small islands. Nuclear power would be too expensive and too risky for the Caribbean.

Mark: 10/16

Examiner commentary: This is a solid Grade III response that demonstrates sound understanding and covers the main assessment criteria. The candidate discusses environmental factors (waste, emissions), economic factors (costs, fuel availability), safety (accidents, hurricanes), and Caribbean context (volcanic islands, no uranium, small scale). A clear recommendation is made with justification. However, the response lacks the depth and detail of a Level 4 answer. Points are stated rather than developed—for example, "nuclear is expensive" without quantifying or explaining why this particularly matters for Caribbean economies. The discussion of safety risks mentions Fukushima and Chernobyl but doesn't develop the connection to Caribbean vulnerability to natural disasters. Some scientific detail is present but could be more precise. The structure is adequate but paragraphs are shorter and less developed than the distinction answer. This represents competent but not outstanding work, achieving approximately 63% of available marks.

Grade V (Near miss) answer

Nuclear power and geothermal both make electricity without producing pollution. They are both better than burning fossil fuels.

Nuclear power is very powerful and produces lots of energy. But it is dangerous because of radiation. If there is an accident, radiation can leak out and hurt people. Nuclear waste is also radioactive for a long time and is hard to get rid of. Nuclear power stations cost a lot of money to build.

Geothermal energy uses heat from volcanoes to make electricity. It is renewable so it won't run out. It is safer than nuclear because there is no radiation. It also doesn't cost as much as nuclear.

For the Caribbean, geothermal is better because some islands have volcanoes. Geothermal is safer and cheaper. Nuclear power would be too dangerous because of hurricanes. If a hurricane hits a nuclear power station, there could be a nuclear explosion. The Caribbean is too small for nuclear power.

I recommend geothermal for the Caribbean because it is renewable, safe, cheap, and some islands have volcanoes to use for geothermal energy.

Mark: 5/16

Examiner commentary: This response falls at the top of Level 2, demonstrating basic knowledge but lacking the development and accuracy required for higher marks. The candidate identifies some relevant points (cost, safety, renewable nature, volcanic resources) but treats them superficially. There is a significant misconception: the statement "nuclear explosion" reveals misunderstanding of nuclear reactor operation—reactors cannot explode like bombs, though they can melt down or release radiation. The environmental discussion is very limited, mentioning only "pollution" without addressing CO₂ emissions or waste disposal issues in detail. Economic analysis is minimal ("costs a lot") without discussing why this matters for Caribbean economies or comparing running costs vs. capital costs. The Caribbean context is mentioned but underdeveloped. The candidate would improve by: (1) developing each point with specific details and explanations, (2) correcting the misconception about nuclear explosions, (3) explicitly addressing all parts of the question (environmental, economic, safety, suitability), and (4) providing more detailed justification linking the evidence to the recommendation.

Question 5(a) — Sample Answers

Grade I (Distinction) answer

In a nuclear fission reactor, energy is released through the splitting of uranium-235 nuclei. The process begins when a slow-moving neutron collides with a uranium-235 nucleus. The nucleus absorbs this neutron and becomes unstable, causing it to split into two smaller daughter nuclei (such as barium and krypton). When the nucleus splits, it releases a large amount of energy in the form of kinetic energy of the daughter nuclei and radiation.

Crucially, when uranium-235 undergoes fission, it also releases two or three additional neutrons. These neutrons can then go on to strike other uranium-235 nuclei, causing them to undergo fission as well. This creates a chain reaction where each fission event triggers further fission events. Control rods made of materials like boron are used to absorb excess neutrons and control the rate of the chain reaction, ensuring it remains steady and doesn't accelerate out of control.

The kinetic energy released by the fission fragments heats up the reactor core. This heat is transferred to water (or another coolant) that flows through the reactor. The water is heated to very high temperatures and turns into high-pressure steam. This steam is then directed through pipes to drive turbines. The turbines are connected to electrical generators, which convert the rotational kinetic energy of the turbines into electrical energy. The steam is then cooled in cooling towers, condensed back into water, and recycled back to the reactor to be heated again.

Mark: 8/8

Examiner commentary: This is an excellent, comprehensive answer that addresses all three bullet points in the question with precision and appropriate detail. The candidate clearly describes the fission process (neutron strikes nucleus, nucleus splits, energy released), explains the role of neutrons in sustaining the chain reaction (neutrons released, strike other nuclei, control rods regulate), and traces the energy conversion pathway from kinetic energy through heat to steam to turbine rotation to electrical energy. The answer demonstrates strong scientific understanding and uses accurate terminology throughout (daughter nuclei, chain reaction, control rods, kinetic energy). This level of detail and clarity is characteristic of Grade I work.

Grade III (Pass) answer

Nuclear fission happens when a uranium-235 nucleus is hit by a neutron. The nucleus splits into two smaller nuclei and releases energy. When the nucleus splits, more neutrons are released. These neutrons hit other uranium nuclei and cause them to split too. This is called a chain reaction and it keeps the reaction going.

The energy that is released heats up water in the reactor. The water boils and turns into steam. The steam spins turbines, and the turbines are connected to generators that produce electricity.

Mark: 5/8

Examiner commentary: This response demonstrates sound basic understanding and hits several key marking points: neutron strikes nucleus, nucleus splits, energy released, additional neutrons released, chain reaction, water heated, steam drives turbines, generators produce electricity. However, it lacks some of the detail required for full marks. The answer could be improved by explaining that 2-3 neutrons are typically released, mentioning what happens to the energy initially (kinetic energy of fragments), and explaining how the chain reaction is controlled. The energy conversion pathway is simplified but acceptable. The terminology is generally correct though less sophisticated than the Grade I answer. This represents competent work earning approximately 63% of available marks.

Grade V (Near miss) answer

In a nuclear reactor, uranium atoms are split apart. This releases lots of energy. The neutrons from one uranium atom hit other uranium atoms and split them too, so the reaction keeps going.

The energy heats water and makes steam. The steam turns turbines which make electricity.

Mark: 3/8

Examiner commentary: This response demonstrates basic awareness of nuclear fission but lacks the detail and precision required for higher marks. The candidate correctly identifies that uranium splits and energy is released, and that neutrons cause further splitting. However, the answer omits crucial details: it doesn't specify uranium-235, doesn't explain that a neutron initiates the process, doesn't mention that the nucleus absorbs a neutron, doesn't describe the daughter products, and doesn't explain how the chain reaction is sustained or controlled. The energy conversion is very briefly stated without showing understanding of the heat transfer mechanism or the role of the generator. To improve, the candidate should: (1) provide more detailed description at each stage of the process, (2) use more precise scientific terminology (nucleus, fission, chain reaction, generator rather than just "make electricity"), and (3) ensure all three bullet points from the question are fully addressed with developed explanations rather than simple statements.