Efficiency
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When is energy considered to be useful?
Energy is only useful when it is transferred from one store to a useful store
Most energy transfers involve some losses. Describe how energy is most commonly lost during an energy transfer.
It is most commonly lost when it is dissipated to the thermal stores of the surroundings, causing a rise in temperature
The diagram shows a motor lifting a load. Describe the energy transfers that occur, and explain how any energy is wasted.
Energy is wasted when the motor transfers energy mechanically to the thermal energy stores of its moving parts, heating the surroundings as the energy is dissipated
What is the equation to calculate efficiency?
(Exam-style question) An electric fan transfers 7250J of energy. 2030J of this is wasted energy. Suggest one way in which energy is wasted by the fan.
One from: • By heating the fan • By heating the surroundings • Transferred away by sound waves