# Direction of magnetic field

## Main Question or Discussion Point

The explanation of this question is much more important to me than just the answer (I have an answer key for this practice test).

Also, if someone could explain the different right hand rules pertaining to E&M and what situation(s) to use each in would be a HUGE help to me. I thought I had it down, but i keep confusing the hell out of myself!

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Doc Al
Mentor
For this situation--the magnetic field surround a current-carrying wire--use the right-hand grip rule. Grip the wire so that your thumb points in the direction of the current--your fingers will be curling around the wire in the direction of the magnetic field.

To solve the problem, you need to add up the field contributions from each current. (Remembering that they are vectors.)

Doc has the basic explanation....or see here: http://en.wikipedia.org/wiki/Right-hand_rule

You'll note that in your example problem some current fields add via the right hand rule and others cancel depending on current direction.....they will cancel when the currents oppose and the distance of point P from those currents are equal.

Born2bwire
Gold Member
This is an obviously ill-posed problem. There is no point C. :p

Doc Al
Mentor
This is an obviously ill-posed problem. There is no point C. :p
:tongue: Yeah, I had meant to point that out, but forgot. I assume it was a typo and that they meant point P.

Redbelly98
Staff Emeritus