A cylindrical cavity of diameter a exists inside a cylinder of diameter `2a` as shown in the figure.
Channel: Doubtnut
Date: 2020-07-05

A cylindrical cavity of diameter a exists inside a cylinder of diameter `2a` as shown in the figure. Both the cylinder and the cavity are infinitity long. A uniform current density `j` flows along the length . If the magnitude of the magnetic field at the point `P` is given by `(N)/(12) mu_(0)aJ`, then the value of `N` is