Suggest one way of discriminating a wire carrying current from a wire carrying no current.

$A$ circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is $ON$. The current as seen from points $A$ and $B$ (in the plane of paper and on the axis of the coil) is anti-clockwise and clockwise respectively. The magnetic field lines point from $B$ to $A$. The $N-$ pole of the resultant magnet is on the face close to

Which instrument is used to convert electrical energy into mechanical energy?

What constitutes the field of a magnet?

Give the factors on which the magnetic field produced by a current-carrying solenoid depends.

Explain briefly different methods of producing induced electromotive force $(emf)$.