# I The origin of self inductance in a current loop?

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1. Nov 10, 2017

### ZeroGravity

Hi Forum

I am trying to get a better grasp of the relation between electric field and the magnetic field.
The overall question is "What is The origin of selfinductance in a current loop?"
Here are my thourghts:

A battery is connected to a say circular wire with some resistance. The current builds up in the magnetic field and the rest as heat in the wire. The energy U in the magnetic field is U=0.5*L*I^2 L being the selfinductance and I the current. The energy in the magnetic field is "returned" then the battery is removed freom the circuit.

But what is the origin og the Induced EMF(ElectroMotoricForce)?

I know from Feynman's lectures Vol II 13.6. that foro two straight wires the magnetic field from wire one, acts on wire two with a force. But viewed from a refrence frame moving with the electrons, the magnetic field is transformed into an electric field, and the force is now seen as a coulomb force.

Is that the same case for a current loop?

What happens if the reference frame rotates?

Thanks all !!
Martin

Last edited by a moderator: Nov 10, 2017
2. Nov 10, 2017

### phyzguy

The induced EMF is due to the changing magnetic field. When the battery is removed from the circuit, the current begins to decay, and so the magnetic field begins to decrease. The changing magnetic field induces an electric field through Maxwells' equation $\nabla \times E =- \frac{\partial B}{\partial t}$

3. Nov 10, 2017

### tech99

To Zero Gravity: And to take a mechanical analogy, the inductor displays "inertia". It is hard to get the current moving and hard to stop it. The inductor stores energy in its magnetic field and in order to stop the current we need to apply a braking force. This is a reverse voltage, which can be obtained by inserting a high resistance, or opening the switch etc.

4. Nov 12, 2017

### jartsa

First take a look at the part titled "Radiation as a Consequence of the Cosmic speed limit" here:
http://physics.weber.edu/schroeder/mrr/MRRtalk.html

And then see the part titled "Compared to the far field" here:
https://en.wikipedia.org/wiki/Near_and_far_field