Case study·Standard multi-step (3/5)·No calculator
Difficulty guide
The label describes the problem, not your ability.
1/5 - Foundational
Warm-up setup; checks one basic idea.
2/5 - Routine exam skill
Normal syllabus skill; usually one main rule or interpretation.
3/5 - Standard multi-step
Exam-style problem with multiple steps or a common trap.
4/5 - Hard exam skill
High-end exam problem; combines methods carefully.
5/5 - Challenge
Stretch problem beyond normal exam pressure.
Question
A model motor rotates briefly but then stops after half a turn. The battery and magnets are working, but the split-ring contacts are not changing connection properly.
Total: 4 marks
(a) Which part is most directly faulty? (1 mark)
(b) What current change should happen after each half turn? (1 mark)
(c) Why can the coil stop if this change does not happen? (2 marks)
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