ELECTRIC CHARGE

2 marks · Hard

Explain why the coulomb (C) is a suitable unit for measuring electric charge. Refer to the definition of current in your answer.

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Because one coulomb is the amount of electric charge that flows past a point when a current of 1 ampere flows for 1 second (Q = I t). It is directly linked to the definition of current.

Must show: 1 C = 1 A × 1 s, Links to current

Also accept: One coulomb is the charge transferred by a current of one ampere in one second.; The coulomb is based on how much charge passes a point in a circuit with a certain current and time.

Common mistakes: Giving definition of ampere instead of coulomb; Not referring to time or current

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Marking points

M1 · 1 mark · States that 1 coulomb is the charge moved by 1 ampere in 1 second, or refers to Q = I t.

M2 · 1 mark · Links the unit to how charge is measured in an electric circuit using current and time.

Worked solution

The coulomb is defined as the amount of charge passing a point in one second when the current is one ampere. So Q = I t: 1 C = 1 A × 1 s.