Re: Induced EMF on loop

[Ludwik Kowalski <kowalskil@MAIL.MONTCLAIR.EDU>]

REPOSTING THE "BOUNCED BACK" MESSAGE.

On Monday, Jan 13, 2003, Savinainen Antti wrote:

>>Kari asked
>
> how is it possible to measure induced emf in a circular loop?
>
> I think that Kari addressed the question in a way that the
> circular loop is *not* cut. When the loop  is moving into a
> magnetic field a changing magnetic flux induces an emf.
> This is a standard high school physics problem: the
> shape of the loop is rectangular, the magnetic field is
> uniform, velocity of the loop is kept constant etc. ...
>
> The problem as I see it, is how to measure the induced
> emf if the loop is not cut. ...

Good question. The problem can be solved, at least in
principle, without using an oscilloscope or a voltmeter.
Suppose the magnetic field through the loop changes
sinusoidally at some frequency, such as 50 or 5000 Hz.
The ac current is flowing and the temperature is going up.

After a certain known number of cycles place the hot
wire into a calorimeter to determine Q, the amount of
thermal energy received. The electric power P can then
be calculated as Q/t, where t is the time of heating.
Knowing the loop resistance R your emf=sqrt(P*R).
This will be the rmf value, I suppose. The amplitude
of the emf would be larger, for example, sqrt(2) times
larger when the magnetic field is being changed
sinusoidally. But I never tried this approach.
Ludwik Kowalski

On Monday, Jan 13, 2003, at 12:28 US/Eastern, Bob Sciamanda wrote:

> Except for the special case where the original induced electric field
> happens to follow the same contour as the loop, charges will
> accumulate on
> the conductor to "properly" direct the current.  There will be electric
> fields and potential differences associated with these separated
> charges.
>
> Bob Sciamanda (W3NLV)
> Physics, Edinboro Univ of PA (em)
> trebor@velocity.net
> http://www.velocity.net/~trebor
> ----- Original Message -----
> From: "John S. Denker" <jsd@MONMOUTH.COM>
> To: <PHYS-L@lists.nau.edu>
> Sent: Monday, January 13, 2003 11:27 AM
> Subject: Re: Induced EMF on loop
> | . . .
> | No, there is no potential, so the concept of "same"
> | potential does not apply for the same reason that
> | "difference" of potential does not apply. . . .