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1.2 Conservation and dissipation of energy

1.2 Conservation and dissipation of energy

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Question 6

Electric motors used in greenhouse ventilation fans are labelled with a power input.

a.

What does the power input of a motor mean? Select one explanation from the list below:

  • The electrical charge transferred by the motor per second.
  • The electric current flowing through the motor.
  • The electrical energy transferred each second to the motor.
  • The electrical potential difference across the motor.
[1]
b.

Write down the equation which links current, potential difference, and power.

[1]
c.

A greenhouse ventilation fan's electric motor has a power input of 90 W90\text{ W}90 W. The power supply potential difference is 24 V24\text{ V}24 V. Calculate the current in the motor.

[2]
d.

The table below shows information about three different electric motors, X, Y, and Z.

MotorTotal power input in wattsUseful power output in wattsEfficiency
X60.060.060.045.045.045.00.750.750.75
Y150.0150.0150.060.060.060.00.400.400.40
Z120.0120.0120.0WWW0.850.850.85

Write down the equation which links efficiency, total power input, and useful power output.

[1]
e.

Calculate the value of WWW in the table.

[2]
f.

In addition to the total power input, electric motors should also be labelled with their efficiency or their useful power output. Suggest why.

[2]
Markscheme

1.2 Conservation and dissipation of energy Questions

  1. GCSE
  2. /Physics
  3. /1.2 Conservation and dissipation of energy

26 exam-style questions on AQA GCSE Physics 1.2 Conservation and dissipation of energy, covering 1.2.1 Energy transfers in a system and 1.2.2 Efficiency. Each one has a worked solution and a mark scheme showing where the marks go.

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