A coaxial cable made up of two conductors. The inner conductor is solid and is of radius `R_1` and the outer conductor is hollow of inner radius `R_2` and outer radius `R_3`. The space between the conductors is filled with air. The inner and outer conductors are carrying currents of equal magnitudes and in opposite directions. Then the variation of magnetic field with distance from the axis is best plotted as

Options

A.
B.
C.
D.

Answer

C

Explanation

From Ampere's law, the field at the axis is zero.
From `x=0` to `R_(1)`, he field increases linearly as the charge enclosed increases.
From `x=R_(1)` to `R_(2)` and from `x=R_(2)` to `R_(3)`, the field decreases hyperbolically but with different slopes as the media are different.