An electron is moving along positive X -axis. To get it moving on an anti-clockwise circular path in X-Y -plane, a magnetic field is applied

Step-by-step solution

For the particle to move along anti-clockwise path, force should be along j y -direction. Since, velocity is along i , Hence, F_m=-e( v B ) In terms of unit vectors, aligned & j =-( i p ) & j = p i aligned Clearly, p = k Hence, magnetic field is applied along positive Z -axis.