# Homework Help: Helmholtz Coil Question

1. Feb 22, 2015

### 8008jsmith

1. The problem statement, all variables and given/known data
I had a lab where we used Helmholtz coils to measure the period of a bar magnet (1/s2) vs output current. The graph of this is a straight line. Using the slope, I am supposed to be able to derive the C constant and then that divided by the intercept is supposed to yield the magnetic field.

2. Relevant equations
(1/s2) = CBtot= C{Bh + .072Nμ0Ic/R} = CBh + C (.072Nμ0/R) Ic

μ0 = 4π x 10-7 T m/A
N = 200 turns
R = 0.105 m
slope = 5.80
intercept = 0.564

C = m/4π2 I
I = moment of inertia
3. The attempt at a solution

I've tried plugging the numbers into the equations to solve for C but I don't know what to use for Ic or I (Moment of inertia). I'm not even sure if this post makes all that much sense since all these variable are based on convention. Any help would be appreciated.

2. Feb 23, 2015

### andrevdh

It seems you have to calculate C from your graph's gradient, which will be equal to
according to you.
Then you use this value of C to get Bh from the y-intercept of the graph.