Homework Help: Electric Current

1. Jan 19, 2012

bb.minhtri

"An electric conductor carrying electric current from left to right is placed in a downward magnetic field. It is observed that there are positive charge on the front of the conductor and negative charge a the back. If the electric current is reverse, flowing from right to left, then the positive charge will appear at the back and negative charge will appear at the front. Determine either negative or positive the free moving charge within the conductor is. "

What kind of phenomenon that cause charge to move at the back and front of the conductor? It does not seem like induction:(
Thank you guys so much for helping:)

2. Jan 19, 2012

Staff: Mentor

Look up the Hall Effect.

3. Jan 19, 2012

SammyS

Staff Emeritus
Hello bb.minhtri. Welcome to PF !

So, you need to determine the sign of the dominant charge carrier in the conductor?

The phenomenon about which you inquired is:
$\vec{F}=q\vec{v}\times\vec{B}\,.$​

4. Jan 19, 2012

bb.minhtri

Thanks, Sammy:D I thought about that formula earlier and there's definitely some force that push the conductor to the front(or to the back). But I still can not figure out its relation with this part It is observed that there are positive charge on the front of the conductor and negative charge a the back. If the electric current is reverse, flowing from right to left, then the positive charge will appear at the back and negative charge will appear at the front.
P/S: PF is so heplful^^ I look up here many times for problems and this is the first time I can not find :D

5. Jan 19, 2012

SammyS

Staff Emeritus
Did you look up the Hall Effect, as gneill suggested?

P/S: I wish that more users of PF would look things up. They often post threads inquiring about problems that have been answered the previous day. We are glad to hear that you find PF helpful.

6. Jan 19, 2012

Staff: Mentor

A current consists of moving charges. Charges moving in a magnetic field experience a force that moves them off their straight-line path. If charge carriers are deflected away from one area and towards another area, a charge imbalance will exist between those two areas, i.e., a potential difference will exist. Look up the Hall Effect.

7. Jan 19, 2012

bb.minhtri

I get it, it's a negative-charge carrier. Sorry gneill, I can't believe I miss your post...
Thank you both so much for helping!