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At the centre of a current-carrying circular coil of radius 5 cm , magnetic field due to earth is 0.5 × 10 - 5 W b m - 2 . The current flowing through the coil, so that it equals the Earth's magnetic field, is

Options

  1. A40   A
  2. B4   A
  3. C0.4 A
  4. D0.2   A

Correct answer

C. 0.4 A

Step-by-step solution

Magnetic field ( B ) at the centre of a coil of radius ( r ) carrying current ( i ) is B = μ 0 i 2 r ⇒ i = 2 r B μ 0 Given, B = 0.5 × 10 - 5 T , r = 0.05 m i = 2 × 0.5 × 10 - 5 × 0.05 4 π × 10 - 7 = 0.398 A ⇒ i ≈ 0.4 A

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