# Homework Help: What directions do the current and electric field point if the electrons move right?

1. Dec 13, 2011

### jauser

1. The problem statement, all variables and given/known data
Electrons move to the right in a certain wire. This indicates that:
a) the current and electric field both point right
b) the current and electric field both point left
c) the current points right and the electric field points left
d) the current points left and the electric field points right
e) the current points left but the direction of the electric field is unknown

2. Relevant equations
don't know any since this is not a computational question?

3. The attempt at a solution
First the current direction would be opposite of the electrons' direction. So then I was using the RHR which has your thumb in the direction of the current. And with that the electric field would point INTO the page.
But the right answer is b), can someone help?

Thank you!

2. Dec 13, 2011

### Stonebridge

Re: What directions do the current and electric field point if the electrons move rig

The RHR is for finding the direction of magnetic fields.
If electrons move to the right then conventional current, which is a flow of positive charge, moves to the left.
The direction of the electric field is the direction of the force on a positive charge.
That is, in this case, the direction of the force that moves the (positive) charges in this wire.
Which way is that?

3. Dec 13, 2011

### jauser

Re: What directions do the current and electric field point if the electrons move rig

That would be the left.
So let me hammer this in my head. Since an electric field came about by the creation of electric charges it will go with the direction of the charge?

Is it (the electric field) ever perpendicular to the charge(s)?

4. Dec 13, 2011

### Stonebridge

Re: What directions do the current and electric field point if the electrons move rig

Yes, the electric field is to the left, in the same direction as the positive charges move.

You can apply an external electric field perpendicular to a beam of electrons, for example, if you want to deflect them.
This is exactly what is done in an oscilloscope to deflect the beam of electrons (cathode rays) up or down, and left to right.

5. Dec 13, 2011

### jauser

Re: What directions do the current and electric field point if the electrons move rig

OK it makes sense now. Thank you very much.

Props!