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JEE Main202227 Jul 2022Morning ShiftPhysicsMagnetic Effects of CurrentActual

Two bar magnets oscillate in a horizontal plane in earth's magnetic field with time periods of 3 s and 4 s respectively. If their moments of inertia are in the ratio of 3 : 2 then the ratio of their magnetic moments will be

Options

  1. A2 : 1
  2. B8 : 3
  3. C1 : 3
  4. D27 : 16

Correct answer

B. 8 : 3

Step-by-step solution

Torque on a bar magnet kept in a magnetic field is given by τ = M B sin θ . Hence, for small oscillations the time period of bar magnets is given by, T = 2 π I M B ⇒ M ∝ I T 2 ⇒ M 1 M 2 = I 1 I 2 × T 2 T 1 2 ⇒ M 1 M 2 = 3 2 × 4 3 2 = 8 3

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