GravitationHard

Question

A long straight wire of radius a carries a steady current i. the current is uniformly distributed across its cross section .The ratio of the magnetic field at a/2 and 2a is

Options

A.1/2
B.1/4
C.4
D.1

Solution

         
Here, current is uniformly distributed across the cros-section of the wire, therforecurrent enclosed in the amperean path
formed at a distance r1
× 1, where I total current
∴ Magnetic field at
P1(B1) =

Now, magnatic field at point P2,
(B2) =
∴     Required Ratio =
     

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