# Solving for magnetic field from a solonoid

1. Jul 27, 2011

### Patdon10

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

The figure below shows a Helmholtz coil used to generate uniform magnetic fields. Suppose the Helmholtz coil consists of two sets of coaxial wire loops with 17 turns of radius R = 76.6 cm, which are separated by R, and each coil carries a current of 0.131 A flowing in the same direction. Calculate the magnitude and the direction of magnetic field in the center between the coils.

http://www.webassign.net/bauerphys1/28-figure-18a.gif

2. Relevant equations

Isn't this a simple solonoid? So can't you just plug in the numbers and get the answers? Or does the multiple connections change the problem?

B = u_0*i*n
n = N/L

3. The attempt at a solution

B= (4*pi*10^-7)*0.131*n
It says r is equal to the length. so, n = N/L = 17/0.766

B= (4*pi*10^-7)*0.131*17/0.766
B = 3.653*10^-6 T, but this is wrong. Can anyone point me in the right direction?

2. Jul 28, 2011

### XCBRA

For this problem yo are trying to calculate the field between the coils. The formula you are using for a solenoid is therfore not valid as it is only valid in the cenetre of a long solenoid. Try treating each coil as a loop of wire of N turns.