Homework Help: Need serious help with right hand rule please for magnetic fields

1. Oct 10, 2011

pyroknife

I have attached the drawing.
Why is the magnetic field at the location negative and not positive? When I do the right hand rule I point my thumb in the direction of the current and wrap my fingers around the wire. My fingers pointed up for each wire which should be positive z not negative, but the answer (teacher said it wasn't wrong) is a negative answer.

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2. Oct 10, 2011

Staff: Mentor

The field around a single conductor consists of circles and concentric circles. For the case in point, for the conductor at y=-6, the circles rise fartherest from you, loop over the top, and sink down between the conductor and you. In the region between the two parallel conductors, the field from the nearest conductor adds to that from the far conductor, being also directed downwards (on the screen). Down is the -z direction. y=-3.8 lies between the two conductors.

3. Oct 11, 2011

pyroknife

Sorry, that was really hard to understand for me. Is there any way you can phrase that using the right hand rule?

4. Oct 11, 2011

pyroknife

I think I'm second guessing myself because of this other problem. I attached it again. The arrows indirect the direction of current travel. I need to find the magnetic field due to the wire at point P. Let's consider the left wire the one with the current pointing up. The magnetic field would be IN TO THE PAGE for that right which is negative? The solution manual had a positive answer for that section of the wire. I'm not sure if these are supposed to be magnitudes, if not, I have no idea how it's positive.

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5. Oct 11, 2011

Staff: Mentor

Your fingers represent the circles, when your whole hand is curled over clutching the conductor. For the conductor in the background, your fingers curl up one side, curl over, and then curl down in the region closest to you.

6. Oct 11, 2011

Staff: Mentor

Negative how? Specify an orientation with reference to the given coordinate system.

Suggestion: take a close look at the depiction of the coordinate axes. Which directions along those axes are positive and which are negative? The x-axis may be the tricky one...

7. Oct 11, 2011

pyroknife

UGHHH it's b/c of the last problem that I started questioning my method. It turns out I did do it right for my original post and the answer was wrong for the one I attached in my post prior to this one.

8. Oct 11, 2011

Staff: Mentor

The field is into the page, but there is no reference here to say which direction is +ve or -ve.

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html" [Broken]

Last edited by a moderator: May 5, 2017