What this practice covers
These questions are drawn from past CIE 9702 Physics papers and filtered to alternating currents. You answer, you find out immediately whether you were right, and you get the reasoning for the correct option and for each distractor. Wrong answers go to a mistakes locker so you can come back to exactly those.
Practice is free. You need an account only so your progress and your mistakes are still there next time.
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What examiners see students get wrong here
These are the errors that cost marks on alternating currents, taken from our own topic notes. Read them before you practise and you will recognise the traps in the questions.
- Reading the peak value off a graph as the peak-to-peak distance.
- Substituting f for ω in x = x₀ sin ωt.
- Quoting a mains supply voltage as a peak value. Quoted supply voltages are r.m.s.
- Putting peak values into P = V²/R and reporting the answer as the mean power. It is the peak power, twice too large.
- Dividing the peak by 2 instead of by √2.
- Saying the mean current over a cycle is the r.m.s. current. The mean current is zero.
- Saying the mean power is zero because the current reverses. Power depends on the square of the current and is positive throughout.
- Drawing half-wave rectification with the negative humps inverted, which is full-wave.
Revise it first
If any of the above is unfamiliar, work through the notes before practising: Alternating currents revision notes.