Q.

A cylindrical conductor of radius R is carrying a constant current. The plot of the magnitude of the magnetic field, B with the distance, d from the centre of the conductor, is correctly represented by the figure           [2019]

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Ans.

(4)

Magnetic field due to long solid cylindrical conductor of radius R,

(i)   For d<R, I'=Id2R2

      B·dl=μ0I'B(2πd)=μ0Id2R2B=μ0Id2πR2

          Bd

(ii)   For  d=R,  B=μ0I2πR (maximum)

(iii)  For  d>R, B=μ0I2πdB1d