Describe an experiment to demonstrate the force acting on a current-carrying conductor placed in a magnetic field.

(N/A) thick,copper wire $AB$ is suspended vertically from a support $T$ by means of a flexible joint $J.$ The lower end $B$ of this wire is free to move between the poles of a $U$-shaped magnet $M.$ The lower end $B$ of the wire just touches the surface of mercury kept in a shallow vessel $V$ so that it can move when a force acts on it. The positive terminal of a battery is connected to end $A$ of the wire. The circuit is completed by dipping another wire from the negative terminal of the battery into the mercury in the vessel. We know that mercury is a liquid which is a good conductor of electricity,so the circuit is completed.
On pressing the switch,a current flows in the wire $AB$ in the vertically downward direction. The wire $AB$ is pushed in the forward direction (towards south) and its lower end $B$ reaches the position $B',$ so that the wire comes to the new position $AB',$ as shown by the dotted line in the figure. When the lower end $B$ of the hanging wire comes forward to $B',$ its contact with the mercury surface is broken,due to which the circuit breaks and the current stops flowing in the wire $AB.$
Since no current flows in the wire,no force acts on the wire in this position and it falls back to its original position. As soon as the wire falls back,its lower end again touches the mercury surface,current starts flowing in the wire,and it is pushed again. This reaction is repeated as long as the current is passed in wire $AB.$ It may be noted that the current-carrying wire is pushed forward because a force is exerted on it by the magnetic field of the $U$-shaped magnet. From this experiment,we conclude that when a current-carrying conductor is placed in a magnetic field,a mechanical force is exerted on the conductor which makes it move.