What this practice covers
These questions are drawn from past CIE 9702 Physics papers and filtered to magnetic fields. 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 magnetic fields, taken from our own topic notes. Read them before you practise and you will recognise the traps in the questions.
- Using the right hand for the motor effect. Left hand for the force on a current, right hand for induction.
- Forgetting that a wire parallel to the field feels no force, or using sin θ where the angle given is to the normal rather than to the field.
- Saying the magnetic force on a moving charge changes its speed. It is always perpendicular to the velocity, so it does no work.
- Defining magnetic flux density without the condition that the wire is at right angles to the field.
- Saying the Hall voltage is bigger in a metal. It is bigger in a semiconductor, because n is smaller.
- Saying like currents repel. Parallel currents in the same direction attract.
- Confusing flux with flux linkage, and leaving N out of an induced e.m.f. calculation.
- Saying an e.m.f. is induced because there is a flux through the coil. It is induced by a change of flux.
Revise it first
If any of the above is unfamiliar, work through the notes before practising: Magnetic fields revision notes.