A student reverses the connections of the battery in a circuit containing a straight current-carrying wire placed above a compass. She notices that the compass needle deflects in the opposite direction compared to before. (i) Why does the needle deflect in the opposite direction? (ii) What does this experiment reveal about the relationship between the direction of current and the magnetic field it produces?
Generated by claude-sonnet-4-6 · 2026-06-26 01:11 · grounding rag
Model Answer
(i) When the battery connections are reversed, the direction of current through the wire also reverses (from south-to-north instead of north-to-south). This reverses the direction of the magnetic field produced around the wire. Since the compass needle aligns with the magnetic field, it deflects in the opposite direction.
(ii) This experiment reveals that the direction of the magnetic field produced by a current-carrying conductor depends on the direction of the current. When the direction of current is reversed, the direction of the magnetic field produced is also reversed.
Source: Chapter 12, Section 12.2, Activity 12.4
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Explanation
- The key idea is the cause-and-effect link: reversed current → reversed magnetic field → opposite needle deflection.
- For part (i), explicitly state why the field reverses (current direction reversed), not just that it does.
- For part (ii), frame it as a conclusion/revelation — examiners expect a generalised statement, not just a description of the activity.
- These two points together are worth 3 marks (approx. 1.5 each), so keep each answer concise but complete.