# Force on a Current-carrying loop

1. Oct 5, 2010

### ninjarawr

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

A rectanglular loop consists of 4 turns of wire carrying a current of 2.7 A. The loop is in the x-y plane, and the direction of flow of the current is shown in the figure. The loop has dimensions a = 1 cm and b = 6 cm. Consider a uniform magnetic field of strength 2.3 × 10-4 T in x, y, or z directions.

If the uniform field of 2.3 × 10-4 T is along the +x axis, find the magnitude of the torque acting on the loop and the total force on side a and b.

Diagram:

2. Relevant equations
t = NIABsin(theta)
B=unI (n= # of turns, u = 4 * 3.14 * E-7)
F=ILBsin(theta)

3. The attempt at a solution
-I found torque using the above equation, and it was 1.49E-6
-Fb is simply 0 because it is parallel to the magnetic field
-but I have NO IDEA how to solve for Fa. I tried using F=ILBsin(theta), (=2.7*.1m*2.3E-4) and it rejects my answer. I also tried =2.7*.1m*2.3E-4*2.

2. Oct 5, 2010

### rl.bhat

you have not used the number of turns in the solution.

3. Oct 5, 2010

### ninjarawr

I did use it to find torque, but did not use it when finding force. how do I use it in the solution? please tell me.

4. Oct 5, 2010

### rl.bhat

It will be 4 times the force on each turn.

5. Oct 5, 2010

### ninjarawr

thanks! that worked for me! But why do we do 4 times for each turn when we are only looking at one side?

6. Oct 5, 2010

### rl.bhat

Because each side contains four terns.

What is torque? FXb. In that calculation you have used no. of terns to calculate the force. Same thing is true for Fa.