In a volume of space that is subject to a changing magnetic field,
there *is* a corresponding electric field. If there's a conductor in
that space, the electric field is present inside the conductor, too.
That's why you can have voltage across the ends of a transformer
winding.
If the current is finite and resistance is 0, then the charge inside
the conductor rearranges itself to create an electric field that
cancels the applied electric field. The net electric field is
therefore zero. Since the electric field is the measured force on a
unit positive charge placed there and an infinitesimally small i.e. 0
force is required to move it because the reistance is zero, then the
electric field has to be zero.
No. Place a coil or loop in a time-varying magnetic field. Connect its
ends to a twisted pair or a coaxial cable and run that cable a mile
away, far from the magnetic field zone, and use the voltmeter there.
Same voltage.
I think the answer is that Faraday's law is true for any passive
region that modifies the electric field, and the electric field in
Faraday's law is the total electric field in the passive region and
not just the induced electric field. So that the electric field
through the terminals of the voltmeter is that due to an
infinitesimally small current that generates a voltage across it's
internal resistance.
Of course, if the voltmeter and its leads are in the field, you'll
have to take the additional potentials into account. In the case of a
voltmeter connected to the secondary of a transformer, the voltmeter
isn't exposed to much field, but it still measures the winding
voltage.
For a finite I , E.dl through 0R leads is still zero, from definition
of what an electric field is.
As noted, you can move the voltmeter far away, out of the field, and
accurately measure the non-zero coil or loop voltage. And a 100-turn
coil pumps move voltage into the meter than a 5-turn coil, or a bigger
loop more than a small one, so there must be voltage within the coil.
Suppose a conductor requires 0.01V applied across it to push 1A
through it. If it is now wound into an inductor and pushes 1A through
1R, the voltage through the 1R will be 1V, and through the inductance
still 0.01V. An electron in the inductance will still require the same
force to move it for the same current, whether that force is from a
static electric field or a changing magnetic field. If the force is
the same, the electric field there is the same.
There *is* an electric field inside a conductor which is immersed
inside a changing magnetic field. "Ohm's law" is trashed by
electrodynamics. The electric field is like a gravitational field...
it permeates everything. If that were not true, every generator and
transformer and motor on the planet would instantly stop working.
The electric field inside a conductor depends on the resistance of the
conductor. But for a conductor of 0 resistance carrying a finte
current it is zero. Concentrate on the definition of an electric
field.
In Hertz's seminal experiments, he detected em fields by using a
single metal wire that *almost* made a full ring, leaving just a tiny
gap. When exposed to a sufficiently strong em field, he observed
sparks jumping across the small gap. No voltmeter needed.
Yes. And the electric field in the gap was several orders of magnitude
greater than that in the metal wire.
Classic electromagnetics.
Well, he makes the point that E.dl through an inductor is zero, yet
you have difficulty understanding why. The paper was written by a
distinguished professor at MIT.
John- Hide quoted text -
- Show quoted text -
Once again, thanks for attempting to discuss my points.
