CAIE IGCSE Physics: Electric Current I = Q/t Question Bank

Practise using I = Q/t to calculate charge, current or time in circuits, lightning strikes, LEDs and oscillating charge transfer.

Exam points

calculate Q, I or t from I = Q/t with units C, A and s kept consistent
convert ms, ns or mA before substituting into charge-current-time calculations
link oscillation frequency or electron number to total charge before finding average current

[Maximum number: 2]

The charge on the sphere in (b) is $+2.0 \times 10^{-5} \mathrm{C}$ . A high resistance wire is now connected between the sphere and earth. It takes 20 minutes for the sphere to become completely discharged through the wire.

Calculate the average current in the wire between the sphere and earth.

average current =

I=Q / t in any form OR Q/t OR $20 \times 10^{-6} /(20 \times 60)$ $1.7 \times 10^{-8} \mathrm{~A}$
OR
I=Q / t in any form OR Q/t OR $20 /(20 \times 60)$ $0.017 \mu \mathrm{~A}$
C1
A1
(C1)
(A1)
Total:

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4.2.2.5—Electric current as charge passing a question 1