A square loop of side $a$ hangs from an insulating hanger of spring balance. The magnetic field of strength $B$ occurs only at the lower edge. It carries a current $I$. Find the change in the reading of the spring balance if the direction of current is reversed

Adjoining figure shows a very long semicylindrical conducting shell of radius $R$ and carrying a current $i$. An infinitely long straight current carrying conductor is lying along the axis of the semi-cylinder. If the current flowing through the straight wire be $i_0$, then the force per unit length on the conducting wire is

Two long parallel wires are at a distance of $1$ metre. Both of them carry one ampere of current. The force of attraction per unit length between the two wires is

A one metre long wire is lying at right angles to the magnetic field. A force of $1\, kg$ wt. is acting on it in a magnetic field of $0.98\, Tesla$. The current flowing in it will be....$A$

A current carrying closed loop in the form of a right angle isosceles triangle $ABC$ is placed in a uniform magnetic field acting along $AB.$ If the magnetic force on the arm $BC$ is $\vec F,$ the force on the arm $AC$ is

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