Q1. [1] § 12.1 MAGNETIC FIELD AND FIELD LINES
Assertion (A) : The needle of a compass, kept in an external magnetic field, always aligns itself in the North-South direction of the Earth.
Reason (R) : The behaviour of the needle of the compass is similar to the behaviour of a freely suspended bar magnet.
- (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
- (C) Assertion (A) is true, but Reason (R) is false.
- (D) Assertion (A) is false, but Reason (R) is true.
Previously asked in CBSE board exam
2026 31/3/1 Q32
Generated by claude-sonnet-4-6 · 2026-06-15 06:47 · grounding rag
Model Answer
(D) Assertion (A) is false, but Reason (R) is true.
The needle aligns along the external magnetic field's direction, not always North-South. However, R is true — a compass needle behaves exactly like a freely suspended bar magnet.
Explanation
- A is false because in an external magnetic field, the compass needle aligns along that field's direction, not Earth's geographic North-South. It aligns N-S only when no other external field is present.
- R is true because the textbook states "A compass needle is, in fact, a small bar magnet," so its behaviour mirrors a freely suspended bar magnet.
- Choose option (D) when the Assertion is wrong but the Reason correctly states a true fact independently.
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