# Magnetic field and parallel current-carrying wires

#### 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 :)

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#### Doc Al

Mentor
could someone please explain why this is so?
How would you apply the right hand rule to find the direction of the magnetic field around a current-carrying wire?

#### ah4p

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

#### Doc Al

Mentor
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?
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.

#### ah4p

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

#### Doc Al

Mentor
one goes into the page and one out of the page?
Nope! Try again. ;)

#### Doc Al

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.)

"Magnetic field and parallel current-carrying wires"

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