(a) How would you demonstrate that a momentary current can be obtained by the suitable use of a magnet, a coil of wire and a galvanometer?

(b) What is the source of energy associated with the current obtained in part (a)?

(a) When there is a relative motion between the coil and magnet, magnetic flux linked with the coil changes. As shown in figure b, the coil is moved towards the north pole of magnet, so the magnetic flux through the coil increases. Similarly, if the coil is moved away from the north pole of magnet, the magnetic flux through the coil decreases.
Due to change in the magnetic flux linked with the coil, an e.m.f. is induced in the coil. The induced e.m.f. causes a current to flow in the coil if the circuit of coil is closed.

(b) the source of energy associated with the current obtained in part (a) is the Mechanical energy spent in moving the magnet relative to the coil.