ELECTRIC CHARGE
4 marks · NormalA current of 0.25 A flows through a wire for 20 s. Calculate the total charge that passes a point in the wire.
If the same amount of charge passed in 10 s instead of 20 s, what would be the new current?
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(a) Q = 0.25 \times 20 = 5\ \mathrm{C} C · must show Substitution into Q = I t, Correct answer with unit
(b) I = Q / t = 5 / 10 = 0.5\ \mathrm{A} A · must show Substitution into I = Q/t, Correct answer with unit
Common mistakes: Switching I and t when using Q = I t; Leaving answers without units
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Marking points
M1 (a) · 1 mark · Correctly uses Q = I t with appropriate values. (follow-through)
A1 (a) · 1 mark · Correct evaluation: 5 C (allow follow-through). (follow-through)
M1 (b) · 1 mark · Uses rearranged formula I = Q/t using answer from (a). (follow-through)
A1 (b) · 1 mark · Correct answer: 0.5 A (allow follow-through from (a)). (follow-through)
Worked solution
(a) Use the formula . Substituting in the values: C.
(b) If the same charge passes in 10 s: A.