NEET 2017 · PhysicsMagnetic momentPrevious Year Question
A 250-turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85 A and is subjected to a magnetic field of strength 0.85 T. The work done for rotating the coil by 180° against the torque is:
Answer: (A) 9.1 J. Answer: (A) Solution: W = MB(cosθ₁ − cosθ₂) with θ₁ = 0°, θ₂ = 180° ⟹ W = 2MB = 2(NIA)B.
- A.9.1 J✓
- B.4.55 J
- C.2.3 J
- D.1.15 J
Correct Answer
(A) 9.1 J
Solution & Explanation
Answer: (A) Solution: W = MB(cosθ₁ − cosθ₂) with θ₁ = 0°, θ₂ = 180° ⟹ W = 2MB = 2(NIA)B. A = 0.021 × 0.0125 = 2.625 × 10⁻⁴ m². M = NIA = 250 × 85 × 2.625 × 10⁻⁴ = 5.578 A·m². W = 2 × 5.578 × 0.85 ≈ 9.1 J. → option A.
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