Hi All.

Stuck on an assignment question on helmholtz coils:

Needing to show that the B on the axis of symmetry at the midpoint between the 2 coils is given by:

B=(0.8)^(3/2)uNI/a

u is mu 0, a is the radius and spacing of the coils.
N turns, and I current.

I cant get where the 0.8 comes from... and the fact that theres 2 coils scares my integration.

Thinking Ampere or possibly Biot Savart - but the symmetry should give me Ampere shouldnt it?

Any help much appreciated.

Thanks.

Ampere's law is useless in this situation, because the required symmetry isn't there. You can't even use it to calculate the field of a current-carrying ring.

Biot-Savart is the way to go. Use it to calculate the field of one ring, then use superposition to get 2 rings. Let me know if you have problems.

Thanks JR.

I found the relevant example in the text.

Tricky how I had to take the reciprocal of 5/4 a^2 twice to get the required answer.

Hope your fud is treating you nicely.