Energy transfers and efficiency (AQA GCSE Physics): Revision Notes

Energy transfers and efficiency

Energy can move from one place to another in different ways. Understanding how energy transfers work helps us make devices more efficient and reduce energy waste.

What is thermal energy transfer?

Thermal energy transfer happens when heat moves from a warm place to a cooler place. The rate at which thermal energy moves through a wall depends on three main factors:

1. Temperature difference

• The bigger the difference between inside and outside temperatures, the faster heat transfers
• For example: If it's 22°C inside and 2°C outside, heat moves quickly through the wall

2. Wall thickness

• Thicker walls slow down heat transfer
• Thin walls let heat through more quickly

3. Thermal conductivity of the walls

• Different materials let heat through at different rates
• This property is called thermal conductivity

Understanding thermal conductivity

Thermal conductivity tells us how good a material is at letting heat pass through it.

• High thermal conductivity = good conductor of heat (like metals)
• Low thermal conductivity = poor conductor of heat (like plastic or wood)

Materials with high thermal conductivity transfer energy faster than materials with low thermal conductivity.

What is efficiency?

Efficiency measures how good a device is at transferring energy into useful forms. All machines waste some energy as heat, so no machine is ever 100% efficient.

The efficiency formula:

$\text{Efficiency} = \frac{\text{useful energy transferred}}{\text{total energy supplied}} \times 100\%$

Reducing energy waste

You can reduce unwanted energy transfers by understanding the main sources of energy loss:

Worked example