Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-L] Lenz's law and conservation of energy

  Lenz's law has nothing to do with conservation of energy. It can be restated as a direct consequence of the Lorentz force law, without any references to magnetic flux. But formulation in terms of flux  is also fine - it emphasizes another aspect of EM interactions: a tendency to conserve flux. As J. Griffiths put it in his textbook: "Nature abhors changes in flux". This is manifest in full sway in superconducting circuits, where the magnetic flux just conserves. But precisely this aspect has not been mentioned among the options a) - d).
   It is easy to show on a simple example of a conducting loop passing through an external magnetic field, that the change of sign in Lenz's law would affect the direction of the induced current, but would not affect conservation of energy. As to conservation of current, there is no such thing at all. There is conservation of charge, but the Lenz law has nothing to do with it, either. So I agree that we have here an ill-posed problem. 

  Moses Fayngold,
  NJIT 


On Wednesday, April 2, 2014 7:24 AM, "Folkerts, Timothy J" <FolkertsT@bartonccc.edu> wrote:

You can heat materials using induced currents.
You can levitate materials using induced currents. 

With a little cleverness, you can do both at once, thereby melting metals without any container!
https://www.youtube.com/watch?v=VydPQuLyEns


________________________________________
From: Phys-l [phys-l-bounces@phys-l.org] on behalf of Bernard Cleyet [bernard@cleyet.org]
Sent: Tuesday, April 01, 2014 8:35 PM
To: Phys-L@Phys-L.org
Subject: Re: [Phys-L] Lenz's law and conservation of energy

On 2014, Apr 01, , at 15:24, Anthony Lapinski <Anthony_Lapinski@pds.org> wrote:

I've wondered about induction cooking ever since a student asked me about
it in class a few weeks ago. So the pans are made of special materials
that heat up, but the stovetop does not?


The stove top is ceramic w/ the RF coil imbedded.  Yes?


Ohms / inch ?!

Give relative efficacy of various metals and frequency, etc.:

Induction cooking - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Induction_cooking

bc

_______________________________________________
Forum for Physics Educators
Phys-l@phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l

_______________________________________________
Forum for Physics Educators
Phys-l@phys-l.org
http://www.phys-l.org/mailman/listinfo/phys-l