Lenz’s Law

Lenz’s law states that:

“The induced current in a loop is in the direction that creates a magnetic field that opposes the change in magnetic flux through the area enclosed by the loop.”

This is a rule devised by the German physicist Heinrich Friedrich Lenz to determine the direction of an induced current in a loop.

Lenz, through his experiments, found out that the current induced through a loop produces its own magnetic field which is referred to as the induced field. This field will then interact with the inducing field either by attraction or repulsion.

For example, consider a loop of wire. As the magnet is moved towards the loop, the magnetic flux increases with a direction going to the loop. The induced current will then tend to oppose the magnetic flux and so the direction of this opposition is opposite to the direction of the magnetic flux. That is, since the direction of the magnetic flux as indicated in the arrow is downward, the direction of the magnetic field produced by the induced current is upward. Using the right-hand rule, with the thumb pointing upward as the direction of the magnetic field by the induced current, the curl of the fingers will then represent the direction of the current which is counterclockwise.

Figure

Now, considering the same loop of wire but the motion of the magnet would be away from the loop. In this case, the magnetic flux decreases with the direction away from the field. If we denote the direction of the flux to be upward, this follows that the direction of the induced current would be downward, meaning it would be towards the plane. Then, using the right-hand rule, with the thumb pointing downward, the curl of the fingers represents the direction of the induced current which is, this time, clockwise.

Figure