An electron moving around the nucleus with an angular momentum l has a magnetic moment 

A thin flexible wire of length $L$ is connected to two adjacent fixed points and carries a current $I$ in the clockwise direction, as shown in Fig.$8.127.$ When the system is put in a uniform magnetic field of strength $B$ going into the plane of the paper, the wire takes the shape of circle. The tension in the wire 

Two circular concentric loops of radii $r_1=20 \mathrm{cm}$ and $r_2=30 \mathrm{cm}$ are placed in the $XY$-plane as shown in Fig.$8.129.$ A current $I=7 \mathrm{A}$ is flowing through them.  The magnetic moment of the loop system is 

A coil of $100$ turns and area $2\times {10}^{-2}{m}^2,$ pivoted about a vertical diameter in a uniform magnetic field carries a current of $5A.$ When the coil is held with its plans north-south direction, it experiences a torque $0.3 Nm.$ When the plane is east-west direction the torque is $0.4 Nm.$ The value of the magnetic induction is (neglect earth's magnetic field)