A straight wire $AB$ of mass $40\,g$ and length $50\,cm$ is suspended by a pair of flexible leads in uniform magnetic field of magnitude $0.40\,T$ as shown in the figure. The magnitude of the current required in the wire to remove the tension in the supporting leads is ...........$A$. (Take $g=10\,ms ^{-2}$ ).

Current flows through uniform, square frames as shown. In which case is the magnetic field at the centre of the frame not zero?

$AB$ and $CD$ are smooth parallel rails, separated by a distance $l$, and inclined to the horizontal at an angle $\theta$ . $A$ uniform magnetic field of magnitude $B$, directed vertically upwards, exists in the region. $EF$ is a conductor of mass $m$, carrying a current $i$, if $B$ is normal to the plane of the rails

A horizontal metallic rod of mass $'m'$ and length $'l'$ is supported by two vertical identical springs of spring of spring constant $'K'$ each and natural length $l_0.$  A current $'i'$ is flowing in the rod in the direction shown. If the rod is in equilibrium then the length of each spring in this state is :-

Figure shows a conducting loop $A D C A$ carrying current $i$ and placed in a region of uniform magnetic field $B_0$. The part $A D C$ forms a semicircle of radius $R$. The magnitude of force on the semicircle part of the loop is equal to

Two thin long parallel wires separated by a distance $b$ are carrying a current $i$ $amp$ each. The magnitude of the force per unit length exerted by one wire on the other is