What is Lenz's law in the context of induction?

Lenz's law states that an induced electromotive force (emf) always generates a current that opposes the change causing it.

Lenz's law is a fundamental principle in electromagnetism, named after the German scientist Heinrich Lenz who formulated it in 1834. It is closely related to the law of conservation of energy. The law is about the direction of induced current and it states that the direction is always such that it will oppose the change in the magnetic field that produced it. This opposition is often referred to as 'back emf'.

Imagine a loop of wire in a magnetic field. If the magnetic field changes, for example by moving a magnet closer to or further from the loop, an emf is induced in the loop. According to Faraday's law of electromagnetic induction, the magnitude of this emf is proportional to the rate of change of the magnetic field. However, Faraday's law doesn't tell us in which direction the induced current will flow. This is where Lenz's law comes in.

Lenz's law tells us that the induced current will flow in such a direction that its magnetic field opposes the change in the original magnetic field. If the original magnetic field is increasing, the induced current will flow in a direction that creates a magnetic field opposing this increase. If the original magnetic field is decreasing, the induced current will flow in a direction that creates a magnetic field opposing this decrease.

This might seem a bit abstract, but it's actually quite intuitive if you think about it in terms of energy. If the induced current didn't oppose the change in the magnetic field, it would be possible to create energy out of nothing, which would violate the law of conservation of energy. By always opposing the change in the magnetic field, the induced current ensures that energy is conserved.

In summary, Lenz's law is a fundamental principle of electromagnetism that describes the direction of an induced current. It ensures that the law of conservation of energy is upheld in electromagnetic systems.