Lenz law : The induced current will appear in such a direction that it opposes the change in the flux in the coil. 

Explanation :

1. We know that when a bar magnet is pushed towards a coil with its north pole facing the coil an induced current is set up in the coil. 

2. Let the direction be clockwise then current carrying loop behaves like a magnet with its south pole facing the north pole of bar magnet. 

3. In such a case, the bar magnet attracts the coil. Then it gains kinetic energy. This is contradictory to conservation of energy. 

4. Hence our assumption is wrong. So correct induced current direction is anti-clockwise.

5. Let us see a case where the bar magnet is pulled away from the coil with the north pole facing the coil. In such case, the coil opposes the motion of bar magnet to balance the conversion of mechanical energy into electric energy. 

6. It happens only when the north pole of the magnet faces the south pole of the coil. 

7. So, the direction of induced current in the coil must be in anticlockwise direction. 

8. In simple terms, when flux increases through coil, the coil opposes the increase in the flux and when flux decreases through coil, it opposes the decrease in the flux. This is Lenz law.