Whenever a magnetic field is changed across the conductor, an e.m.f. induces across it which becomes the cause of induced electric current. If a bar magnet is pushed in to a coil, an e.m.f. is induced in the coil and induced electric current flows through it as shown below.
If a bar magnet is pulled out of the coil, again an e.m.f. induces across the coil and induced electric current flows through it but in this case the direction of the current reverses as shown below.
The magnitude of induced e.m.f. and of course induced electric current can be increased by the following way:
- Using a strong magnet (increasing the strength of magnetic field).
- Increasing the number of turns in the coil.
- moving he magnet faster
Note: If the bar magnet is kept inside the coil at rest, no magnetic lines of forces will be cut (i.e. magnetic field will not be changed across the conductor), so no e.m.f. will be induced.