# Gauss's Law for Magnetism

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

## 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!

## The Attempt at a Solution

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## Answers and Replies

rl.bhat
Homework Helper
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.

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Dick
Science Advisor
Homework Helper
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?

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