Net force on rectangular circuit

1. Sep 6, 2015

Alameen Damer

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

2. Relevant equations
Right hand rules

3. The attempt at a solution
Am i correct for a? I drew my interpretations of the magnetic field around each section.
For b) am i correct to think the internal net force in the rectangular wire is 0, and the only force acting on it is that of the long wire at the bottom. And if that is correct, which way is the net force acting on the rectangular loop?

2. Sep 6, 2015

Titan97

For part a, all your forces have to be in opposite direction.
F=i (L×B)
For the bottom part, L is along $-\hat i$ and B is along $\hat k$.
L×B is along $-\hat j$ or downwards.

Last edited: Sep 6, 2015
3. Sep 6, 2015

Alameen Damer

Why are they in opposite directions? Does that not fit the right hand rule?

4. Sep 6, 2015

rude man

yes
where is the B field stronger, nearer the long wire or farther away from it?

5. Sep 6, 2015

Alameen Damer

Near the long wire, then it must be acting downwards correct?

6. Sep 6, 2015

rude man

Since you previously showed that you could determine the direction I'm giving you a "Yes".

7. Sep 6, 2015

Alameen Damer

Ok, are the directions of the magnetic field around the rectangle wrong?

8. Sep 6, 2015

rude man

They're wrong.
Set up a coordinate system x to the right, y up, z out of page. Then evaluate the various unit vectors.
E.g. for the top left segment we get i x -k = ?
Learn the circular +/- i +/- j+/- k ↔ +/- i diagram for the signs. I find it a whole lot easier than twisting my hand and fingers into unnatural shapes ....