Induced Electric Field

Induced EMF 's can be created when nothing is moving. In this case the qvB part of the Lorentz Force is zero and only leaves the qE part to place a force on a charge. The induced E is caused by a changing magnetic field according to Faraday's Law:

As with Ampere's law, there is a connection between the direction of curve the path integral of E is taken around and the direction of the normal to the surface for the magnetic flux. Your right thumb represents the direction of dA and the fingers of your right hand curl in the direction of the path. When your right thumb points in the direction opposite to the change in B your fingers curl in the direction of the induced electric field.


A B-field points into the screen, and it is getting stronger. Find the direction of the induced E-field.

Your thumb on your right hand should point out of the screen, opposite to the B-field which is getting stronger.

Which way do your fingers curl? What does the electric field line look like?

Show me.

What is the strength of the E-field at a radius r from the center?

Use Faraday's law.

1) Choose a path for the electric field - in this case the path is a circle
2) Evaluate the path integral - from the symmetry E is constant along the circular path
so

3) Evaluate the rate of change in the flux:

4) Equate E and B:

Go to Point Charges.


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