O Level Physics: Energy Resources and Efficiency — Practice Questions

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Energy Resources revision notes and the full study guide, which covers biofuels and the complete power-generation table.

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Questions

1. Classify each as renewable or non-renewable: coal, wind, nuclear, tidal, natural gas, geothermal. [3]

2. Explain why nuclear power sits awkwardly in this classification. [2]

3. Describe how electricity is generated in a fossil-fuel power station, naming the energy transfers at each stage. [4]

4. A power station burns fuel supplying 2000 MJ each second and generates 700 MJ of electrical energy.

(a) Calculate the efficiency. [2] (b) Calculate the energy dissipated each second. [1] (c) (Background, not examinable — the specification requires only the two efficiency equations, not Sankey diagram construction.) Describe how this would be shown on a Sankey diagram. [3]

5. (Extension beyond the strict 5054 scope — a real-world evaluation question, rather than the syllabus’s restricted “advantages/disadvantages” comparison, which excludes cost and reliability.) Evaluate solar power for a remote village with no grid connection, considering reliability, cost and environmental impact. [6]

6. Explain why a fossil-fuel power station cannot be 100% efficient. [2]

7. A kettle rated at 2.2 kW is used for 3.0 minutes.

(a) Calculate the energy transferred in joules. [3] (b) (Cross-topic — specific heat capacity is a thermal physics outcome, not part of this energy resources and efficiency subtopic.) It heats 0.80 kg of water by 65 °C. Calculate the useful energy. (c = 4200 J kg⁻¹ °C⁻¹) [2] (c) Calculate the efficiency. [2]

8. State the three factors the syllabus expects you to compare when discussing the advantages and disadvantages of an energy resource. [3]

9. For each of hydroelectric power, biofuels and solar (photovoltaic) power, state whether it generates electricity using a turbine driven by steam, a turbine driven directly by moving water or air, or neither. [3]

10. Explain why biofuels, although renewable, generate electricity in essentially the same way as a fossil-fuel power station. [3]

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Answers

1. Renewable: wind, tidal, geothermal [1] [1]. Non-renewable: coal, nuclear, natural gas — coal and natural gas because they are fossil fuels, nuclear because uranium is finite [1].

2. It is non-renewable, since uranium is a finite resource [1], but it is not a fossil fuel and produces no carbon dioxide in operation, so it does not fit the usual renewable/fossil grouping — it sits in a category of its own [1].

3. Fuel is burned, transferring energy from the chemical store to the thermal store of the water [1]. The water boils to steam, which turns a turbine — thermal store to kinetic store [1]. The turbine turns a generator, which converts this kinetic energy into electrical energy carried by the electrical transfer pathway, not a further energy store [1]. This electrical energy is then transferred to consumers through the National Grid [1].

4. (a) efficiency = useful output ÷ total input = 700 ÷ 2000 [1] = 0.35 or 35% [1]. (b) 2000 − 700 = 1300 MJ [1]. (c) (Background, not examinable.) A single arrow of width proportional to 2000 MJ enters from the left [1]; a useful output arrow of 700 MJ continues horizontally [1]; a branch of 1300 MJ representing dissipated thermal energy leaves downwards, with every arrow’s width drawn strictly to scale [1].

5. Reliability: solar is intermittent — it produces nothing at night and less in cloud [1], so batteries are needed for a continuous supply [1]. Cost: high initial installation cost [1] but no fuel cost and very low maintenance thereafter, which suits a remote site where fuel delivery would be expensive [1]. Environmental: no emissions in operation [1]; manufacturing the panels has an environmental cost, and land is required [1].

6. Some energy is always dissipated to the surroundings as thermal energy [1] through friction in the turbine, heat lost in the cooling towers and in the exhaust gases, so useful electrical output is always less than the chemical energy supplied [1].

7. (a) E = Pt = 2200 × 180 [1] [1] = 396 000 J [1]. (b) E = mcΔθ = 0.80 × 4200 × 65 [1] = 218 400 J [1]. (c) 218 400 ÷ 396 000 [1] = 0.55 or 55% [1].

8. Whether the resource is renewable [1]; when and whether it is available (e.g. daylight, weather, tide times) [1]; and its impact on the environment [1] — the syllabus deliberately limits the comparison to these three.

9. Hydroelectric — turbine driven directly by falling/flowing water, no steam stage [1]. Biofuels — burning heats water to steam, driving a steam turbine [1]. Solar (photovoltaic) — neither; radiation is converted to electricity directly, with no turbine or generator involved [1].

10. Biofuels release chemical energy on burning, just like a fossil fuel [1]; this energy heats water to steam in a boiler, and the steam drives a turbine connected to a generator, exactly as in a fossil-fuel station [1]. Being renewable only describes how the fuel is replaced (regrown plant or waste material), not the method used to generate the electricity itself [1].

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Where marks are usually lost

• Classifying nuclear as renewable, or as a fossil fuel.
• Omitting an energy transfer stage in the power station description.
• Not drawing Sankey arrow widths to scale (background — Sankey diagrams are not on the 5054 specification).
• Forgetting to convert kW to W or minutes to seconds.
• Bringing in cost or general reliability when the question asks specifically for the syllabus’s three permitted factors: renewable, availability, environmental impact.
• Saying every renewable resource skips the turbine and generator — only solar photovoltaic does; hydroelectric, wind, tidal and wave power still use a turbine, just driven directly rather than by steam.