# Homework Help: Gauss's Law for Magnetism

1. Nov 20, 2007

### yeo

Question:
http://web.ics.purdue.edu/~yeo/phys1.jpg [Broken]

Formula: (Gauss's Law for Magnetism)
Line integral of[B dot nhat(perpendicular unit vector) * deltaA] = 0

3. The attempt at a solution
So, if there is a bar magnet inside, the side arrows are pointing in the wrong direction, so I ruled that out.

A magnetic monopole will have all arrows emanating from the center or all pointing towards the center, so I ruled that out.

The total flux is not 0, so there has to be something in it?

->That left me with only 2 other choices, but I've tried all combinations of them and none of them are correct. Any help guys? I only have 2 more tries left and its due tomorrow....

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

2. Relevant equations

3. The attempt at a solution

Last edited by a moderator: May 3, 2017
2. Nov 21, 2007

### rl.bhat

The fourth choice is correct, because if you keep a current carrying coil inside it will also have the lines of magnetic fields entering and leaving.

Last edited: Nov 21, 2007
3. Nov 21, 2007

### Dick

The flux through the box is nonzero. You are right, there is 'something' inside it. If you believe the flux. But we know of no magnetic sources (i.e. monopoles). And a current carrying wire is NOT A SOURCE. It has div(B)=0. Conclusion?

Last edited: Nov 21, 2007