Efficiency

Question 1

When is energy considered to be useful?

Answer 1

Energy is only useful when it is transferred from one store to a useful store

Question 2

Most energy transfers involve some losses.

Describe how energy is most commonly lost during an energy transfer.

Answer 2

It is most commonly lost when it is dissipated to the thermal stores of the surroundings, causing a rise in temperature

Question 3

The diagram shows a motor lifting a load.

Describe the energy transfers that occur, and explain how any energy is wasted.

Answer 3

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

Question 4

What is the equation to calculate efficiency?

Answer 4

Question 5

(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.

Answer 5

One from:

• By heating the fan
• By heating the surroundings
• Transferred away by sound waves