Re: Lenz's Law

[Barlow Newbolt <NewboltW@WLU.EDU>]

There are those on the list who can give a much better treatment of
this, but I will put in my two cents worth.  The current in the loop
alters the magnetic field in the region of the wire and this altered
field changes the characteristics of the current in the wire.  You are
dealing with mutual induction and you are right that there are induced
emf's in the wire and in the loop.                              WBN

> > > Leinoffs@ACC.SUNYACC.EDU 03/22/00 09:40AM >>>
Can someone help me out and check my reasoning.

Given: a long straight wire lying on a horizontal table carrying
conventional
current north.  Next to the wire, on the right, is a metal ring lying
flat on
the table.

If the current in the wire is increased, there will be a growing
B-field inside
the metal ring directed down into the table.  This should (I'm pretty
sure)
induce a counter-clockwise current in the ring which will cause a
B-field up out
of the table in opposition to the change in field that induced the
current in
the first place (Lenz's Law?)

What bothers me is that (by my understanding is that by Lenz's law)
this induced
current in the ring should somehow oppose the increasing current in the
wire,
and I don't see the mechanism for that.  If the ring was part of a
circuit with
resistance, the induce current would do work, which would mean that it
would
take more work to increase the current in the straight wire when the
loop was
present than without the loop.

What mechanism would make increasing the straight wire current more
difficult
with the wire loop there?

Stu Leinoff
Adirondack Community College