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The magnetic field within a long, straight solenoid with a circular cross-section of radius r is (as shown) increasing at a rate of α . The rate of change of flux through a circle with radius a inside the solenoid, normal to the axis of the solenoid and with centre on the solenoid axis is

Options

  1. A2 πa 2 α
  2. B1 2 πa 2 α
  3. Cπa 2 α
  4. D3 2 πaα

Correct answer

C. πa 2 α

Step-by-step solution

Rate of change of flux through circle with radius a dϕ m dt = A dB dt = πa 2 α

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