GCSE Energy — Stores, Transfers, Efficiency and Resources Explained

Energy is one of the most fundamental concepts in GCSE Physics, and it links every other topic together. Understanding energy stores and transfers, performing efficiency calculations, and evaluating energy resources are all separately assessed skills. This guide covers every aspect of the GCSE energy topic with full worked examples.

Energy Stores

Energy is not created or destroyed — it is transferred between stores. The key energy stores at GCSE:

• Kinetic energy store: Energy due to motion. KE = ½mv²
• Gravitational potential energy store: Energy due to position in a gravitational field. GPE = mgh
• Elastic potential energy store: Energy stored in stretched or compressed springs/materials. EPE = ½ke²
• Thermal energy store: Energy stored in the random motion of particles. Increases with temperature.
• Chemical energy store: Energy stored in chemical bonds (e.g. fuel, food, batteries).
• Nuclear energy store: Energy stored in atomic nuclei, released in fission and fusion.
• Electrostatic/magnetic energy stores: Energy stored in electric or magnetic fields.

Energy Transfer Pathways

Energy is transferred between stores via pathways. The four main pathways:

• Mechanically: By a force acting over a distance (e.g. pushing a box, stretching a spring)
• Electrically: By charge flow through a component
• By heating: By conduction, convection or radiation (infrared)
• By radiation: By electromagnetic waves (light, IR, etc.)

Key Energy Equations

Specific Heat Capacity

Specific heat capacity (c) is the energy needed to raise the temperature of 1 kg of a substance by 1°C. Different materials require different amounts of energy for the same temperature change — water has a very high specific heat capacity (4,200 J/kg°C), which is why it takes a long time to heat and cool.

Example: How much energy is needed to heat 2 kg of water from 20°C to 100°C? Q = 2 × 4200 × 80 = 672,000 J = 672 kJ.

Efficiency

No energy transfer is perfectly efficient — some energy is always dissipated (usually as heat) to the surroundings. Efficiency measures what proportion of input energy is usefully transferred.

Example: A motor receives 500 J of electrical energy and does 350 J of useful work. Efficiency = 350/500 = 0.7 = 70%. The remaining 150 J is wasted as heat due to friction.

Energy Resources

Renewable energy resources can be replenished naturally and will not run out on a human timescale. Non-renewable resources took millions of years to form and will eventually be depleted.

Non-Renewable Resources

• Fossil fuels (coal, oil, natural gas): Burn to produce heat → steam → turbine → generator → electricity. Reliable and controllable but produce CO₂ (greenhouse gas) and other pollutants. Will eventually run out.
• Nuclear fuel (uranium, plutonium): Fission produces heat → steam → turbine → generator. Very high energy density, no CO₂ during operation, but produces long-lived radioactive waste and risk of accidents.

Renewable Resources

• Solar: Photovoltaic cells convert light directly to electricity. No fuel cost, no emissions, but dependent on sunlight and intermittent.
• Wind: Wind turns turbines. No emissions, but intermittent and visual/noise impact.
• Hydroelectric: Water falling through turbines generates electricity. Reliable and controllable, but requires flooding of valleys — habitat destruction.
• Tidal: Tidal flow drives turbines. Predictable and reliable, but expensive infrastructure and limited suitable locations.
• Geothermal: Heat from the Earth's interior used to generate steam. Reliable and very low emissions, but limited to volcanically active regions.
• Biomass: Burning biological material (wood, crop waste). Carbon-neutral in theory (CO₂ released was absorbed during plant growth), but produces particulates and requires large land area.

The AQA energy specification is at the AQA GCSE Physics specification page.