Electromagnetism: Can someone please explain Lenz's Law?

Question

My textbook (in a suspiciously conspiratorial voice): Lenz's Law states that any induced current in a loop will be in the direction such that the flux it creates will oppose the change in the flux that produced it.

Me: *blink*

My textbook: *evil laugh*

Answer 1

Lenz's Law:

*SPELL MY NAME WITH A 'Z'. NOT AN 'S'.*

Answer 2

Yes it is a word and yes it is included.

So you have a loop.

And the B-flux changes through the loop and induces a current.  Which way will the current go?

If you have current going through a loop, that creates a B-field.  If you put your right thumb in the direction of the current, your fingers curl in the direction of the B-field.  Notice that the current causes the B-field to go one way inside the loop and the other way outside of the loop.

So suppose your loop is in the xy plane.  Suppose the magnetic flux is in the +z direction and is increasing.  That means that the current will be in the direction to create a magnetic field inside the loop in the minus-z direction.  As we look down at the xy plane from the +z direction (as we usually do), that means the current will be CLOCKWISE.  Put your thumb along the loop clockwise.  See how your fingers point into the paper--opposing the increasing flux.  If the flux were decreasing or increasing in the minus-z direction, then the current would be counterclockwise.  When you put your thumb counter-clockwise, your fingers curl around so they are going up (+z direction) inside the loop.

Make sense?

Answer 3

Lenz's law is fundamental in being able to determine which direction the resulting EMF is, due to a change in magnetic flux (faraday)

Basically the direction of the EMF is such that it OPPOSES THE CHANGE IN FLUX, for example, if the flux is decreasing with time, the EMF will act to increase the flux (retain equilibrium), and vice versa

This is a general description, M. Bekki has an accurate geometrical description.