If one moves a magnet next to its coil, the moving magnet induces an electromagnetic force in its coil. The current induced in the coil due to the motion of the magnet along the coil is called induced current.
Scientist Lenz provided a formula to determine the direction of the current flowing in his coil. This is known as Lenz’s formula. This law is also called the third law of electromagnetic induction. The formula is – “In any electromagnetic induction, the induced electromagnetic force or direction of current flow is such that, as soon as it is produced, it inhibits the cause that produced it.”
In other words, “the dominant force or direction of flow is such that it opposes or obstructs all causes that create it.” The mathematical form of the formula is:
Lenz’s Law and Conservation of Energy
As a result of electromagnetic induction, we see that current is produced in a closed coil without a source of electromagnetic energy. Apparently this seems to be an exception to the law of conservation of energy. But in fact, there is no phenomenon against the law of constancy of force in electromagnetic induction. We can prove this from Lenz’s formula.
As we know from Lenz’s theorem, the electromagnetic force in a coil inhibits the cause of its creation. A relative motion between a coil and a magnet gives rise to an induced current in the coil which opposes that relative motion. So some mechanical energy is always expended to maintain that speed. It is this mechanical energy that is converted into electrical energy and creates current flow in the coil. So the magnetic action of current obeys the law of conservation of force.