Re: [Phys-l] induced emf and induced current

["LaMontagne, Bob" <RLAMONT@providence.edu>]

I was running off to work when I responded to this. Let me give a more complete response while I have a break.

________________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of carmelo@pacific.net.sg [carmelo@pacific.net.sg]
Sent: Tuesday, October 13, 2009 1:51 AM
To: phys-l@carnot.physics.buffalo.edu
Subject: Re: [Phys-l] induced emf and induced current

Quoting "LaMontagne, Bob" <RLAMONT@providence.edu>:
> I'm not sure what is meant by "the induced emf could be considered
> as towards the centre". The induced emf, as I understand it, is the
> result of integrating the induced electric field around a closed
> path encompassing a changing magnetic field. It doesn't really exist
>  from point to point because magnetic flux cannot be defined
> relative  to an open path.

The induced emf for this spinning disc is B(pi)r^2 (frequency). There
is a voltage difference between the rim and the centre of the disc.

> I'm not sure the differential approach helps either, i.e., curl E =
> -dB/dt, because the integral of the curl from point to point along
> an open path doesn't have a physical meaning (that I am aware of).

For open path, there can be induced emf or potential difference. The
physical meaning could be "Hall voltage", and the measured voltage may
depend on the orientation of your voltmeter.


Best regards,
Alphonsus

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