# Direction of electric field

1. Mar 30, 2014

### Queequeg

1. The problem statement, all variables and given/known data

In a circular region in the plane of paper, a magnetic field is directed out of the page and decreasing. What is the direction of the electric field at a point to the right of the region?

2. Relevant equations

Lenz's law

3. The attempt at a solution

Since the magnetic field is decreasing, Lenz's Law states the induced magnetic field will oppose this change, so the induced magnetic field will also point out of the page. So to the right of this region, the right hand rule says that the electric field should point towards the top of the page, but the answer in my key is to the bottom. Am I wrong?

2. Mar 30, 2014

### Simon Bridge

The magnetic field is out of the page and decreasing - this would correspond to a south pole facing the page and being drawn away ... so the page should have an induced north pole there, because it wants to pull it back.

Which would put the current circulating anti-clockwise.
Current follows the electric field - so you seem to be right.

You could also work it from $\nabla\times\vec E = -\frac{\partial}{\partial t}\vec B$

3. Mar 30, 2014

### rude man

I agree with posts 1 and 2.