[Physics] Faraday’s law. And Faraday’s law of induction

classical-electrodynamicselectromagnetic-inductionelectromagnetism

Can anyone properly tell me the difference between the two, and which one historically came first.

A majority of sources directly connect "emf" to flux but the 'flux rule' isn't absolute. It isn't universal. It has been generally interpret as flux creates emf. But it seems more natural to me to say that a changing magnetic field produces an electric field (everywhere in the universe however small) whose curl is nothing but change in flux.

Is it true that changing magnetic fields creates an electric field? (that need to be in a conductor. )

Griffiths' is the book which gave me this conclusion but everywhere else I have looked so far (Irodov, The Feynman Lectures, University Physics (by Zemansky) and even the MIT online lecture on induction by Walter Lewin) have said otherwise.

Best Answer

(a) As far as I know, Faraday's law in electromagnetism is another name for Faraday's law of induction.

(b) You refer to the equation $$\vec{\text{curl}}\ \vec{E}=-\frac {d \vec{B}}{dt}.$$ Applying Stokes's theorem (and taking the differentiation outside the integral sign) this integrates to $$\oint \vec{E}.d\vec{s}=-\frac{d}{dt} \int_S \vec{B}.\vec {dS}$$ The left hand side is the line integral of the electric field, that is the induced emf, in a closed loop enclosing an area S, and the right hand side is the rate of change of magnetic flux through S, so we have $$\text{emf in loop = –rate of change of flux through loop.}$$ So the difference implied in your second paragraph between the curl equation and "emf = – rate of change of flux" isn't a difference at all!

(d) All this is valid whether or not there is a conductor.

The betatron is a particle accelerator that can be understood in terms of an induced emf in a non-conducting toroidal chamber. You could argue, I suppose, that the presence of electrons being accelerated in the chamber makes it a conductor! But it would be weird, wouldn't it, for the emf suddenly to appear when electrons are injected into the chamber?

(e) The equation "emf = – rate of change of flux" can, though, also be applied to a moving conducting loop cutting flux, though this time the emf arises from magnetic Lorentz forces driving charge carriers around the loop.

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