Physics307L:People/Klimov/Eoverm
e/m Ratio Lab Summary
In this lab, the charge to mass ratio of the electron was measured. The experiment was based on the fact that moving electrons feel a force in the presence of a magnetic field, which causes them to spin. So, in this experiment, electrons were accelerated into a magnetic field, and the radius of the resulting circular beam was measured. Using the values of the radius, the accelerating voltage of the electrons and the current flowing through the coils, the e/m ratio was calculated.
Important Links:
It was discovered that there were many potential systematic sources or error in this experiment. This is reflected in our final result, given that our mean e/m ratio was found to be:
[math]\displaystyle{ \frac{e}{m}_{exp}=3.3142 \cdot 10^{11} \frac{C}{kg} }[/math]
with a standard deviation of:
[math]\displaystyle{ \sigma = 0.31407 \cdot 10^{11} \frac{C}{kg} }[/math]
while the actual is:
[math]\displaystyle{ \frac{e}{m}_{act}=1.7563 \cdot 10^{11} \frac{C}{kg} }[/math]
giving us a percent error of:
[math]\displaystyle{ %_{error} = 88.70% }[/math]
This mean was obtained by averaging the e/m ratios of all measured data points. WIth each measurement, there was also an uncertainty that resulted from our limited ability to measure the radius of the beam correctly. While these uncertainties are represented in the figures that I have posted in the lab notebook, I have chosen not to report them here -- there were so many possible sources of error that it would not be reasonable to account for only one of them numerically in this summary.
References
1. Helium. Used to find ionization energy. Given in kJ/mol, and then converted.
2. NOAA. Used to find the earth's magnetic field in Albuquerque.
