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## Homework Statement

Sorry to bother you guys,

I've heard that Ampere's Law is either ineffective for calculating the B field due to a circular loop or needs some modification (I wasn't sure which).

I'm trying to figure out why this doesn't work so I can get a better understanding of Ampere's Law. I have attached a picture of two loops (probably trivial). The inner loop is the one with a current the outer loop is the surface I chose for Ampere's Law.

I know you guys have to deal without a lot of dang so I hope I haven't imposed too much.

Thanks,

## Homework Equations

(integral) Bdl = u * I

## The Attempt at a Solution

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To be more concrete about this whole thing imagine I had a looped wire with current I. I will now use Ampere's Law. First I will choose a surface which is another circular loop that contains the first loop. Now I will use:

(integral) B dl = u * I. Since each piece of current in the loop has another piece of current going in the opposite direction (it's a circle after all). I should get an I enclosed of 0. This would suggest the B field is zero (which I could justify using the Biot-Savart law isn't true). For space I will not do that here; that's a number plugging game.