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 a2 and 2a from its axis is

Solution

## For a point inside the solid cylinder, Bins=μoir2πa2 at r=a2B1=μoi4πa For a point outside the solid cylinder Bout=μoi2πr At r=2aB2=μoi4πa⇒B1B2=1

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