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Re: Induced EMF on loop



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