# Force between two wires

1. Oct 12, 2005

### jena

Hi,

My Question:

A rectangular loop of wire lies in the same plane as a straight wire, as show in Fig. 20-57. There is a current of 2.5A in both wires. Determine the magnitude and direction of the net force on the loop.

http://www.webassign.net/pse/p31-09.gif" [Broken]

where the width is 10.cm and width of the box is 5.0 cm and distance from the rectangular loop and the straight wire is 3.0 cm.

My Work

F=((mu constant)(I)^2(length))/(2pi(distance))
F=((4pi x 10^-7 Tm/A)(2.5A)^2(.10m))/(2pi(.05m))
F=2.5 x 10^-6 N

but the answer in the back of the book gives F=2.6 x 10^6

What did I do wrong

Thank You

Last edited by a moderator: May 2, 2017
2. Oct 12, 2005

### Tom Mattson

Staff Emeritus
You need to calculate the force on each segment of the loop due to the long straight wire, and add them up. It looks to me like you only attempted to calculate the force on a single segment.

It also looks like you've plugged in the wrong distance (that's supposed to be the distance from the straight wire to the segment you are analyzing).

And this bit here is confusing:

Which one is the "width"?

3. Oct 12, 2005

### jena

Sorry,

http://www.webassign.net/pse/p31-09.gif" [Broken]

width=5 cm
Length= 10 cm
height= 3 cm

I thought the width would be used for the distance, but I guess that's wrong. I tried plugging in number but with no results close to the textbook answer of 2.6 x 10^-6 N

I still don't know what I did wrong though