# Magnetic field and parallel current-carrying wires

1. Feb 13, 2015

### ah4p

could someone explain question 10. JUST PART b)iii)

http://mrmackenzie.wikispaces.com/file/view/AHpastpaper2004.pdf

I got the magnitude of the magnetic field
but I don't know how to find its directionI thought it might be to do with left and right hand rule?

could someone please explain why this is so?

thank u v much in advance :)

[Moderator note: Moved to new thread; removed bits of old thread from this post]

Last edited by a moderator: Feb 13, 2015
2. Feb 13, 2015

### Staff: Mentor

How would you apply the right hand rule to find the direction of the magnetic field around a current-carrying wire?

3. Feb 15, 2015

### ah4p

I don't know

using the left hand rule (I'm Scottish so I use negative current) surely the magnetic field due to one wire is up and due to the other one is down so they'd cancel?

4. Feb 15, 2015

### Staff: Mentor

It does say electron flow, so you're good with a left rule. (Although I recommend always using a right hand rule and positive current.) Realize that the current in each wire goes in opposite directions. Describe the direction of the magnetic field surrounding each wire.

5. Feb 15, 2015

### ah4p

one goes into the page and one out of the page?

6. Feb 15, 2015

### Staff: Mentor

Nope! Try again. ;)

7. Feb 15, 2015

### Staff: Mentor

Note: It's not completely clear which wire is closest to the viewer. I will assume that the wire appearing lowest in the diagram is closest to the viewer. (Use whatever makes sense to you, just state what assumptions you are making.)