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Electricity and Circuits

Energy transferred by moving charge

  • 3 things to know
  • Paper 2

Overview

The energy, charge and potential difference equation with calculations, why a higher voltage transfers more per coulomb, and the two conditions for a current to flow in a circuit.

What you need to know

Answer each one before you reveal it.

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Key term

Why must a circuit be complete and contain a cell for current to flow, and why does a lamp light the instant a switch closes?

Key term

Which equation links energy transferred, charge moved and potential difference?

Key term

A charge of 20 C moves through a potential difference of 12 V. How much energy is transferred?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Which equation links energy transferred, charge moved and potential difference?

    Model answer

    Energy transferred in joules equals charge moved in coulombs multiplied by potential difference in volts.

  2. 2

    A charge of 20 C moves through a potential difference of 12 V. How much energy is transferred?

    Model answer

    The energy transferred is 20 C × 12 V = 240 J.

  3. 3

    A lamp transfers 600 J when 50 C of charge passes through it. What is the potential difference across the lamp?

    Model answer

    The potential difference is 600 J ÷ 50 C = 12 V.

  4. 4

    A torch bulb runs from a 4.5 V supply and transfers 90 J. What charge has passed through the bulb?

    Model answer

    The charge is 90 J ÷ 4.5 V = 20 C.

  5. 5

    A current of 2 A passes through a motor for 30 s with 6 V across it. How much energy is transferred?

    Model answer

    The charge is 2 A × 30 s = 60 C, so the energy transferred is 60 C × 6 V = 360 J.

  6. 6

    Why does the same charge transfer more energy in a 230 V heater than in a 12 V heater?

    Model answer

    Each coulomb transfers an amount of energy equal to the potential difference, which is 230 J per coulomb rather than 12 J.

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