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Electricity and Circuits

Power as energy transferred per second

  • 2 things to know
  • Paper 6

Overview

Power as the energy transferred each second, the watt, comparing appliances by rating, and the equation linking power, energy and time with calculations.

What you need to know

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Key term

What is meant by power?

Key term

What unit is power measured in, and what is its symbol?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is meant by power?

    Model answer

    Power is the energy transferred each second.

  2. 2

    What unit is power measured in, and what is its symbol?

    Model answer

    Power is measured in watts, symbol W.

  3. 3

    What does a power of one watt mean in terms of energy?

    Model answer

    One watt means that one joule of energy is transferred every second.

  4. 4

    A lamp is marked 60 W. How much energy does it transfer each second?

    Model answer

    It transfers 60 J each second.

  5. 5

    Which transfers energy faster, an appliance rated 500 W or one rated 2000 W?

    Model answer

    The 2000 W appliance, because it transfers 2000 J each second rather than 500 J.

  6. 6

    Which equation links power, energy transferred and time?

    Model answer

    Power in watts equals energy transferred in joules divided by time taken in seconds.

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Watt means the unit of power, symbol W.
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