Conservation of Energy — Energy Stores & Transfers | IGCSE Physics

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 10% of your exam marks.

stable

Medium

Stable10%

GPE, KE and efficiency calculations are core calculation questions in every series.

The principle

The states:

Energy cannot be created or destroyed; it can only be transferred from one store to another.

For any closed system, the total energy across all the stores stays constant
Energy is never truly lost, but it can be (spread out) into the surroundings by heating or radiation; once dissipated, it is wasted because the original task cannot reclaim it

Useful and wasted energy

Every real transfer produces a mixture of:
- Useful energy in the store the designer wanted (the kinetic store of the moving fan, the thermal store of the food)
- Wasted energy spread around the surroundings (heating from friction, sound carried away into the air, infrared radiation off hot casings)
The total of useful + wasted output always equals the input, which is conservation of energy in practice

Exam tip

Conservation of energy

Stating the principle of conservation of energy is a 1-marker, so you need to know energy cannot be created or destroyed, only transferred from one store to another. Both halves — "created" and "destroyed" — are needed; "energy cannot be lost" alone doesn't score.

Worked example

Calculating kinetic energy

A 4 kg ball rolls along a surface at 6 m/s. Calculate its kinetic energy.

Solution:

Write the formula: KE = ½ × mass × speed²
Substitute: KE = ½ × 4 × 6²
Square the speed first: 6² = 36
KE = ½ × 4 × 36 = 2 × 36 = 72 J