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Concepts Of Physics MCQ Edition [Volume 2]PhysicsPermanent Magnets

In an oscillation magnetometer, a bar magnet completes 40 oscillations per minute. A completely demagnetized identical magnet is then placed over the first magnet in the magnetometer. Determine the time required for this combination to complete 40 oscillations, neglecting any induced magnetism.

Options

  1. A2 minutes
  2. B2 minutes
  3. C4 minutes
  4. D1 2 minutes

Correct answer

B. 2 minutes

Step-by-step solution

The time period of oscillation of a bar magnet in a uniform magnetic field is given by T = 2 I MB , where I is the moment of inertia and M is the magnetic moment. Let the initial moment of inertia be I and the magnetic moment be M . The time taken for 40 oscillations is t₁ = 1 minute. When an identical demagnetized magnet is placed over the first one, the total moment of inertia becomes I' = I + I = 2I . The magnetic moment remains M' = M since the second magnet is demagnetized and induced magnetism is neglected. T

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