# Torque

Discussion in 'Homework Help' started by mo2015mo, Jul 23, 2013.

1. ### mo2015mo Thread Starter Member

May 9, 2013
157
1
Hi Guys,,

how i can determine the loop's surface normal for my attached problem and for any loop?? what's the rule??

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2. ### WBahn Moderator

Mar 31, 2012
23,552
7,207
Draw a diagram from above so that you are looking down the edge of the plane of the loop. Then figure out the normal.

Or, find two vectors that lie in the plane of the loop and then take the cross product, which yields a vector that is normal to both of the vectors in the plane.

You have to decide which direction to use and for that rely on the right-hand rule.

The obvious vectors to use are the vectors of two sides of the loop:

v1 = z^

v2 = sinθ x^ + cosθ y^

By the right hand rule, if we cross v1 into v2 we will have a vector consistent with the direction of the current in the loop

v1 x v2 = (0 - cosθ)x^ + (sinθ - 0)y^ + (0 - 0)z^
v1 x v2 = -cosθ x^ + sinθ y^

mo2015mo likes this.
3. ### mo2015mo Thread Starter Member

May 9, 2013
157
1
I finished the EM1 course and got A+ grade.

________WBahn________
Thanks for all your efforts to help me get this done.

Mar 31, 2012
23,552
7,207