0
\$\begingroup\$

Hoping somebody can set me straight on the magnetic fields involved in an inductor when the current is changing. This is how I see it:

The source current has a magnetic field. This changing flux produces an EMF which in turn produces a current which also has a magnetic field which opposes the change which produced it. The lenze induced magnetic field would have opposite polarity to the inducing magnetic field.

So therefore there are two magnetic fields:

  1. Magnetic field from source current
  2. Magnetic field as a result of Lenz Law (cemf).
\$\endgroup\$
  • \$\begingroup\$ From the Ampere's law, we know that the current in the conductor product the Magnetic field. And this change in the Magnetic field "induced voltage" in the inductor (Faraday's law). And this voltage, by definition (Lenz Law), opposes any external effort to change the existing flux (or current) in an inductor.electronics.stackexchange.com/questions/288380/… \$\endgroup\$ – G36 Jul 6 '18 at 13:30
  • \$\begingroup\$ It's the back emf (due to a changing current) that opposes a change in the current. \$\endgroup\$ – Andy aka Jul 6 '18 at 15:54
0
\$\begingroup\$

Hoping somebody can set me straight on the magnetic fields involved in an inductor when the current is changing.

As we want to study the inductor under changing current conditions, we'll drive it with a current source.

This is how I see it:

The source current has a magnetic field. This changing flux produces an EMF which in turn produces a current ...

No, the EMF produced by the changing flux produces a voltage at the inductor's terminals. This voltage results in power flowing into the inductor as a result of the current flow. It's this demand for power that does the Lenz 'opposition' of the change in current. In the case of driving from a current source, this does not result in any change in current in the inductor.

If on the other hand, we had an inductor that we could move a magnet in and out of, then moving the magnet would change the flux and generate a terminal voltage. If there was a load, or a short circuit across the terminals, this would allow a current to flow, which would oppose the movement of the magnet, drawing power from the magnet motion and delivering power to the electrical load on the inductor.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.