How is energy stored, transferred and conserved, and how do we measure power and efficiency?
Energy stores and transfers, the conservation of energy and dissipation, the kinetic and gravitational potential energy equations, power as the rate of energy transfer, efficiency, and renewable and non-renewable energy resources.
A focused CCEA GCSE Single Award Science answer on energy, covering energy stores and transfers, conservation and dissipation, the kinetic and gravitational potential energy equations, power, efficiency, and renewable and non-renewable energy resources.
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What this dot point is asking
CCEA wants you to describe energy stores and transfers, state the conservation of energy and explain dissipation, use the kinetic and gravitational potential energy equations, calculate power and efficiency, and compare renewable and non-renewable energy resources.
Energy stores and transfers
Conservation and dissipation
The energy equations
Power and efficiency
Energy resources
Examples in context
Example 1. Why a bouncing ball does not return to its start height. When a ball is dropped, gravitational potential energy transfers to kinetic energy. At each bounce some energy is dissipated as heat and sound (in the squashing of the ball and air resistance), so less energy is left for the next bounce, and the ball rises a little lower each time. The total energy is still conserved; it is just spread to the surroundings.
Example 2. Choosing an energy resource. Wind power is renewable and releases no carbon dioxide while running, but it only works when the wind blows and the turbines are costly to build. A gas power station gives reliable power on demand, but burns a non-renewable fuel and releases carbon dioxide. Weighing reliability, cost and environmental impact like this is exactly the kind of evaluation CCEA asks for when comparing energy resources.
Try this
Q1. State the principle of conservation of energy. [1 mark]
- Cue. Energy cannot be created or destroyed, only transferred from one store to another.
Q2. Calculate the kinetic energy of a 2 kg object moving at 3 m/s. [2 marks]
- Cue. J.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA SAS 20203 marksA 0.5 kg ball moves at 4 m/s. Calculate its kinetic energy. (Use kinetic energy equals one half times mass times speed squared.)Show worked answer →
Three marks for the formula, the substitution and the answer.
Kinetic energy equals one half times mass times speed squared.
KE equals 0.5 times 0.5 times 4 squared, which is 0.5 times 0.5 times 16.
That gives 4 J.
So the kinetic energy is 4 J. Markers reward squaring the speed (not doubling it), the correct substitution and the unit joules.
CCEA SAS 20194 marksAn electric motor takes in 200 J and does 150 J of useful work. Calculate its efficiency and explain what happens to the rest of the energy.Show worked answer →
Four marks for the efficiency calculation and the dissipation point.
Efficiency equals useful energy output divided by total energy input.
Efficiency equals 150 divided by 200, which is 0.75, or 75 percent.
The other 50 J is dissipated to the surroundings, mostly as heat (and some sound), because of friction.
The energy is not destroyed; it is spread out and is no longer useful, in line with conservation of energy. Markers reward the correct efficiency and that the wasted energy is dissipated as heat, conserving the total.
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Sources & how we know this
- CCEA GCSE Science: Single Award specification — CCEA (2017)