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JEE Main20209 Jan 2020Morning ShiftPhysicsMagnetic Effects of CurrentActual

A long, straight Wire of radius a carries a current distributed uniformly over its cross-section. The ratio of the magnetic fields due to the wire at distance a 3 and 2 a , respectively from the axis of the wire is:

Options

  1. A2 3
  2. B2
  3. C1 2
  4. D3 2

Correct answer

A. 2 3

Step-by-step solution

B A = μ 0 i r 2 π a 2 = μ 0 i a 3 2 π a 2 = μ 0 i π a 2 a 6 = μ 0 i 6 π a B B = μ 0 i 2 π 2 a B A B B = 4 6 = 2 3

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