A long straight wire of radius a carries a steady current I The current is uniformly distributed over its cross-section. The ratio of the magnetic fields B and B', at radial distances a2 and 2a respectively, from the axis of the wire is

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Detailed Solution

Magnetic field at a point inside the wire at distance r=a2 from the axis of wire is B=μ0I2πa2r=μ0I2πa2×a2=μ0I4πaMagnetic field at a point outside the wire at distance r(=2 a) from the axis of wire isB'=μ0I2πr=μ0I2π×12a=μ0I4πa ∴ BB'=1

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