Gouy Balance Nonlinear Slope (Magnetic Susceptibility Lab)

[djh101]

I am currently analyzing my data for the physical chemistry magnetic susceptibility lab. All the data is giving nice, smooth graphs for force vs. current, but I am unable to linearize them.

$F = \frac{1}{2}\chi\mu_{0}AH^{2}$

I have plotted force vs. current and force vs. current squared (current should be proportional to field, so using current shouldn't affect the slope). The former gives an upward moving curve while the latter gives a downward moving curve, so neither is linear. However, fitting a second degree polynomial gives a very good fit to the former (R² = .997) and a near perfect fit to the latter (R² = .999). What might be a possible explanation for the nonlinearity?

The only thing I can think of would be an inaccurate current reading, but even doubling the current (making it higher than the current setting, which was already higher than the actual current) doesn't completely kill of the nonlinearity. Any ideas?

http://onlinesciencetools.com/_miscfiles/nicl2.png

 

[Nino MMP]

It is possible that the nonlinearity is due to a non-linear relationship between current and the magnetic field. This could be caused by the magnetic core material having non-linear properties, or due to the experimental setup. For example, if the wire is wound too tightly, it can cause a non-linear relationship between the current and the magnetic field. It is also possible that the nonlinearity is due to the fact that the magnetic susceptibility of the sample is changing with the increasing field strength, which would cause a non-linear response in the force measurement.