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## Homework Statement

A short, straight wire segment of length l carries current I and is oriented so that it makes an angle of 30° with the horizontal. Point P is a distance r below the wire segment.

Which expression below is the best approximation for the magnetic field caused by the wire segment at point P?

http://online.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?courses/phys212/oldexams/exam2/fa09/fig15.gif

(a) (μoIlcos30°) / (4π^2)

(b) (μoIlsin30°) / (4π^2)

(c) (μoIl) / (4π^2)

## Homework Equations

d

**B**= (μo Id

**l**x

**r(unit vector)**) / (4πr^2)

## The Attempt at a Solution

It seems I have to integrate to get the answer, however the geometry behind this problem is really confusing me. I believe I have to integrate r from when it touches the beginning of the wire segment to the end of the wire segment, however I can't figure out how to manipulate the Biot-Svart law to do that. This is what I have so far:

(μo I)/(4π) = S sin(theta)ds/r^2 (S = integral :p)

Now, what do I do with ds?

Can anyone help me out, help would be greatly appreciated :]!

Btw π = pi and μo = mu(0), don't know if you can tell.

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