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Re: Explaining Lenz's Law



Tina Fanetti wrote:

My calc based physics class is covering Lenz's law.
They get that the law is about the inducing a current
which causes an opposite induced magnetic field.

That's all there is to Lenz's "law".
End of discussion.

They want to use the right hand rule to figure out the
direction of this induced current.

That's an entirely separate question. (One of the few
nice things about Lenz's law is that it doesn't require
use of any right-hand rule.)

One book uses your fingers, another book uses the thumb
for current. One book throws an area vector in the direction of your thumb.

For a loop of current how do you know which way the palm of your hand faces...

There are three equally-good answers. Pick one.

Fact: If (X,Y,Z) is a right-handed basis then
any cyclic permutation of (X,Y,Z) is also a right-handed
basis. Or to say the same thing in the current context, any
cyclic permutation of the right hand's (fingers, palm, thumb)
is a right-handed basis.

The following versions appeal to me for their mnemonic
value. Using right hand:
-- Curl your fingers. Circular motion in the direction the
fingers are pointing will advance a right-hand screw in the
direction the thumb is pointing.
-- Similarly: Fingers initially coplanar with palm; this is
the X direction. Fold fingers 90 degrees, now normal to palm;
this is the Y direction. Thumb is Z direction.
-- Fingers represent ("look like") field lines. Velocity
of positively-charged object in direction of thumb. Force
in direction of palm ("push with palm").