Calculating efficiency (in terms of energy and power)
I can calculate the efficiency of an energy transfer and describe ways in which energy is dissipated.
Calculating efficiency (in terms of energy and power)
I can calculate the efficiency of an energy transfer and describe ways in which energy is dissipated.
Slide deck
Lesson details
Key learning points
- Energy is dissipated due to friction which causes particles to vibrate more quickly and heats up the surroundings.
- Energy is dissipated due to drag which causes particles in the surroundings to move more quickly.
- Efficiency = useful output energy transfer / total input energy transfer
- Efficiency = useful power output / total power input
- Efficiency can be increased by lubrication, bearings or wheels.
Common misconception
Pupils may not realise that energy transfers usually result in the heating of the surroundings and therefore some energy ends up in a thermal store.
Pupils should have opportunity to identify and describe places in a system where energy is dissipated and transferred into a thermal store.
Keywords
Dissipate - Friction can cause energy to dissipate (spread out and becomes unusable) into the surroundings, causing them to heat up.
Efficiency - Efficiency is the fraction of energy supplied to an object or system that is usefully transferred by it.
Useful output energy transfer - The amount of energy usefully transferred by an object or system is the useful output energy transfer.
Total input energy transfer - The total amount of energy transferred to an object or system is the total input energy transfer.
Equipment
A selection of balls that bounce, a metre ruler, masking tape.
Content guidance
- Equipment requiring safe usage.
Supervision
Adult supervision recommended.
Licence
This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
Video
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Worksheet
Starter quiz
6 Questions
1500 W
3.4 kJ
340 J
0.015 kW