Solving Ampere's Law Trouble: My Mistake in Calculating B?

[giladsof]

Where is my mistake? I have a feeling it's in the calculation of B... ?

 

[ehild]

Do you mean that B is constant inside the rectangle?

ehild

 

[giladsof]

It's a given that the rectangle is fixed to the ground..

So apart from the fact that the magnetic field in it changes direction all the time, B's size is constant

 

[ehild]

So you say that the magnetic field of a current carrying wire does not depend on the distance from the wire?

ehild

 

[WatermelonPig]

For a long straight wire, B is proportional to 1/r.