First slide
Magnetic field due to a straight current carrying wire

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


Magnetic field at a point inside the wire at distance 

r=a2 from the axis of wire is 


Magnetic field at a point outside the wire at distance r(=2 a) from the axis of wire is

B'=μ0I2πr=μ0I2π×12a=μ0I4πa   BB'=1



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