# CBSE Class 12-science Answered

Plot and explain the graph for variation in magnetic field due to current through a long circular cylinder as we go from a point on the axix of cylinder to apoint lying outside it.

As we know, the magnetic field due to current through a long circular cylinder, at apoint inside the cylinder is given as

_{}

Clearly, the magnetic field inside the wire B=const times r, so it is proportional to r. It is zero for a point on the axis of cylinder, and an increase linearly with increasing distance from the centre of the wire. It is maximum for a point on the surface of cylinder.

On the other hand, the magnetic field outside is given as, _{}