# Homework Help: Force between an infinitely long wire and a square loop

1. Feb 3, 2008

### xinlan

1. The problem statement, all variables and given/known data

A square loop of wire with side length a carries a current I1 . The center of the loop is located a distance d from an infinite wire carrying a current I2. The infinite wire and loop are in the same plane; two sides of the square loop are parallel to the wire and two are perpendicular as shown.

1. What is the magnitude, F , of the net force on the loop?
I got that one, which is
F= I1*a*uo*I2*((1/2pi(d-0.5a)-(1/2pi(d+0.5a))

2. The magnetic moment m of a current loop is defined as the vector whose magnitude equals the area of the loop times the magnitude of the current flowing in it (m=IA), and whose direction is perpendicular to the plane in which the current flows. Find the magnitude, F , of the force on the loop from Part A in terms of the magnitude of its magnetic moment.
Express in terms of m,I2 ,a ,d , and uo .

2. Relevant equations

3. The attempt at a solution
F= I1*a*uo*I2*((1/2pi(d-0.5a)-(1/2pi(d+0.5a))
since m=I/A, then I= m/A
F = (m/A)*a*uo*I2*((1/2pi(d-0.5a)-(1/2pi(d+0.5a))

Did I do it correct?

Thank you..

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2. Feb 3, 2008

### Staff: Mentor

Get rid of the A. It equals a^2.

3. Feb 3, 2008

### xinlan

thank you Doc Al.. :)