Q1. [1] § 12.2.2 Right-Hand Thumb Rule
Assertion (A) : Direction of force exerted on a current-carrying conductor placed in a magnetic field remains same if the directions of both magnetic field and current flowing through the conductor are reversed.
Reason (R) : The direction of force exerted on a current-carrying conductor placed in an external magnetic field can be determined by using magnetic compass.
- (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 31/2/1 Q32
Generated by claude-sonnet-4-6 · 2026-06-15 06:47 · grounding rag
Model Answer
(C) Assertion (A) is true, but Reason (R) is false.
Assertion is true: by Fleming's left-hand rule, reversing both current and field simultaneously keeps the force direction unchanged. Reason is false: the direction of force on a current-carrying conductor is determined by Fleming's left-hand rule, not a magnetic compass.
Explanation
- Assertion check: Fleming's left-hand rule shows force direction depends on both current and field. Reversing both reverses each factor twice, so the net force direction is unchanged. ✓
- Reason check: A magnetic compass detects/maps magnetic field direction, not the force on a current-carrying conductor. The correct rule for force direction is Fleming's Left-Hand Rule. So Reason is false.
- Examiners award this mark only for choosing (C) with a valid brief justification. Just writing the option letter without reasoning may risk losing the mark in some schemes.
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