Deriving Magnetic Field from Helmholtz Coil Lab Data | Homework Question

[8008jsmith]

Homework Statement

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.

Homework Equations

(1/s²) = CB_tot= C{B_h + .072Nμ₀I_c/R} = CB_h + C (.072Nμ₀/R) I_c

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

The Attempt at a Solution

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I've tried plugging the numbers into the equations to solve for C but I don't know what to use for I_c 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.

 

[andrevdh]

It seems you have to calculate C from your graph's gradient, which will be equal to

C (.072Nμ0/R)

according to you.
Then you use this value of C to get B_h from the y-intercept of the graph.