A conducting circular loop of radius $r$ carries a constant current $i$. It is placed in a uniform magnetic field $\overrightarrow B $, such that $\overrightarrow B $ is perpendicular to the plane of the loop. The magnetic force acting on the loop is

A circular loop has a radius of $5\, cm$ and it is carrying a current of $0.1\, amp$. Its magnetic moment is

A rigid wire consists of a semicircular portion of radius $R$ and two straight sections. The wire is partially immerged in a perpendicular magnetic field $B=B_0\ {j}$ as shown in figure. The magnetic force on the wire if it has a current $i$ is :

A beam of electrons and protons move parallel to each other in the same direction, then they

Suppose an isolated north pole is kept at the centre of a circular loop carrying a electric current $i$. The magnetic field due to the north pole at a point on the periphery of the wire is $B$. The radius of the loop is $a$. The force on the wire is

An arrangement of three parallel straight wires placed perpendicular to plane of paper carrying same current $'I'$ along the same direction as shown in figure. Magnitude of force per unit length on the middle wire $'B'$ is given by