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 sensor resistance is placed as one arm of a Wheatstone bridge arranged so that at balance. When the sensor is heated, its resistance increases slightly.
Total: 4 marks
(a) Find the initial sensor resistance if it is opposite the 30 ohm arm and the balance condition is . (2 marks)
(b) What happens to the galvanometer current after the sensor resistance increases? (1 mark)
(c) Name the circuit principle that makes this small resistance change detectable. (1 mark)
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