Re: [Phys-L] Lenz's law
INteresting discussion here! I somed drop the ND magnet down a copper pipe
in my HS classes.
I am reminded of a scary demo I saw at a summer AAPT meeting some 30 years
ago. I have notes and have to go through to find who did it and when. But
it was an axe on a pivot which was released and the metal blade went
through a powerful electromagnet, which slowed/stopped by the motion. The
kicker was that you put your hand at the bottom! So the presenter showed us
a few times that it worked, and then asked for a volunteer! People in the
room literally moved away! And then a man decided to try. Everyone was
cringing and nervous. What if the power went out? It did work! I will try
to find who did this. It's in my notes for all the meetings I ever attended
over the years.
On Mon, Apr 29, 2024 at 9:41 AM John Denker via Phys-l <
phys-l@mail.phys-l.org> wrote:
> Hi --
>
> I would emphasize the "voltage equals flux dot" law before
> going anywhere near Lenz's law.
>
> The former is quantitative and is a direct corollary of the
> Maxwell equations. It has thousands of quantitative as well
> as qualitative applications.
>
> This stands in contrast to Lenz's law, which is merely
> qualitative.
>
> When applied to a perfectly or near-perfectly conducting loop,
> it makes it obvious why the sign of Lenz's law has to be as
> it is.
>
> There is a wonderful hands-on demo you can do to illustrate
> this, if you have a big powerful magnet available.
>
> I added whole new section of my writeup, talking about this
> and outlining where it comes from. Maxwell equations plus
> Stokes's theorem.
>
> https://www.av8n.com/physics/straight-wire.htm#sec-flux-dot
>
> It's very new so there are probably typos and such. Possibly
> missing steps in the argument. Let me know if you have questions
> or suggestions.
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