OCR GCSE Physics B (Twenty First Century)
OCR GCSE Physics B P2 Sustainable Energy Exam Questions
Free OCR GCSE Physics B revision for P2 Sustainable Energy: what you need to know, common mistakes and exam-style questions with answers. Covers energy use, power, kilowatt-hours, efficiency, energy resources, generating electricity, renewables, the National Grid, transformers and mains electricity.
Practise P2 Sustainable Energy with past papers
Once you have learnt this topic, find the P2 Sustainable Energy questions in real OCR GCSE Physics B past papers and mark them with the mark scheme. Doing lots of real questions is the quickest way to learn how examiners ask about each idea.
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About OCR GCSE Physics B P2 Sustainable Energy
Chapter P2 looks at how much energy we use and how we can supply it sustainably. On OCR Physics B you calculate energy transferred from power and time, including in kilowatt-hours, work out efficiency and compare the costs of running appliances. You then compare renewable and non-renewable energy resources, learn how electricity is generated and distributed through the National Grid, and study mains electricity in the home. The chapter links to climate change in P1 and to electric circuits and generators in P3. Examiners often set cost calculations, efficiency questions and evaluations of different power stations using data.
What you need to know
- P2.1 Energy and power Energy transferred = power x time, in joules (W and s) or kilowatt-hours (kW and h). Cost = energy in kWh x price per kWh.
- P2.1 Efficiency Efficiency = useful energy transferred / total energy transferred, often given as a percentage. Wasted energy is usually dissipated to the surroundings as heating.
- P2.2 Energy resources Fossil fuels and nuclear fuel are non-renewable; wind, solar, hydroelectric, tidal, wave and biofuels are renewable. Compare them on reliability, cost, carbon dioxide emissions, land use and how quickly they can respond to demand.
- P2.2 Generating electricity Most power stations heat water to make steam that drives a turbine connected to a generator. Wind and hydroelectric power turn turbines directly, while solar cells produce electricity directly.
- P2.2 The National Grid Step-up transformers raise the voltage for transmission so the current is lower, reducing energy lost heating the cables; step-down transformers lower it for homes. UK mains is alternating current at 230 V and 50 Hz, with live, neutral and earth wires.
Common mistakes in P2 Sustainable Energy
- Mixing units in energy calculations. Use kW and hours to get kWh, or W and seconds to get joules.
- Writing an efficiency above 1 or 100%. Check you divided useful energy by total energy, not the other way round.
- Saying high voltage transmission is more efficient because it is faster. It is more efficient because the lower current reduces heating in the cables.
- Calling nuclear power renewable. Uranium is a finite resource, although nuclear power stations produce very little carbon dioxide.
- Saying wasted energy is destroyed. Energy is conserved; wasted energy is dissipated to the surroundings.
Try three P2 Sustainable Energy exam-style questions
1. A 2 kW heater is used for 3 hours. Electricity costs 30p per kWh. Calculate the cost. (3 marks)
Show the mark scheme answer
Energy = power x time = 2 x 3 = 6 kWh; cost = 6 x 30; = 180p (£1.80).
2. A motor is supplied with 200 J of energy and does 50 J of useful work. Calculate its efficiency. (2 marks)
Show the mark scheme answer
Efficiency = 50 / 200; = 0.25 or 25%.
3. Explain why electricity is transmitted across the National Grid at very high voltages. (3 marks)
Show the mark scheme answer
A step-up transformer increases the voltage; for the same power the current is lower; a lower current means less energy is lost heating the cables, so transmission is more efficient.
P2 Sustainable Energy FAQs
What does OCR Physics B P2 Sustainable Energy cover?
It covers energy use and costs, power, efficiency, renewable and non-renewable resources, how power stations generate electricity, the National Grid and mains electricity.
Which paper is it examined in?
OCR Physics B has two papers at each tier, Breadth in physics and Depth in physics, and both can assess content from every chapter, so P2 can appear on either paper.
How do I answer evaluate questions on energy resources?
Use the data given, compare at least two resources on both advantages and disadvantages (cost, reliability, emissions, environmental impact) and finish with a justified conclusion.
