Edexcel GCSE Combined Science CP3 and CP8 Energy: a complete overview of energy stores, conservation, work, power and efficiency

What CP3 and CP8 actually demand

Energy is one of the central ideas of GCSE physics, examined across both papers. The examiners reward correct use of the stores-and-transfers language, the kinetic and gravitational potential energy calculations, the work, power and efficiency equations, and a balanced comparison of energy resources.

This guide walks through both topics and ties together the matching dot-point pages, each with its own practice questions.

Energy stores, transfers and conservation

Energy is held in stores (kinetic, gravitational potential, elastic, thermal, chemical) and moved by transfers (mechanical, electrical, heating, radiation). Conservation of energy says energy is never created or destroyed, only transferred or dissipated. The key calculations are:

When energy is transferred, some is dissipated to the surroundings as heat and becomes less useful.

Work, power and efficiency

• Work done: $W = F \times d$ (energy transferred by a force).
• Power: $P = \dfrac{E}{t}$, in watts (joules per second).
• Efficiency: useful output / total input, always less than 1.

Energy resources

Non-renewable (fossil fuels, nuclear) will run out; renewable (wind, solar, hydroelectric, tidal, wave, geothermal, biomass) are replenished. Renewables release little carbon dioxide but are often less reliable.

How CP3 and CP8 are examined

• Calculations. Kinetic and gravitational potential energy, work, power and efficiency.
• Conservation. Tracking energy through transfers (for example a falling object).
• Dissipation. Explaining wasted energy and how to reduce it.
• Resources. Comparing renewable and non-renewable resources.

Check your knowledge

A mix of recall and calculation questions covering CP3 and CP8. Attempt them under timed conditions, then check against the solutions.

1. State the principle of conservation of energy. (1 mark)
2. Write the equation for kinetic energy. (1 mark)
3. Calculate the kinetic energy of a 2 kg object moving at 5 m/s. (2 marks)
4. Write the equation for work done. (1 mark)
5. Write the equation for power. (1 mark)
6. A device supplies 200 J and does 150 J of useful work. Calculate the efficiency. (2 marks)
7. Why is no device 100% efficient? (1 mark)
8. Give one example of a renewable energy resource. (1 mark)