Physics307L:People/Carrillo/e/m Ratio

e/m Lab Summary

• Please note that Ginny was my lab partner for this lab.

Purpose

The purpose of this lab was to measure the chare-to-mass ration of an electron by measuring the radii of the electron beam in the presence of a magnetic field that is produced by the Helmholtz coils. We measured the radii at different currents and voltages.

Calculations and Analysis

We calculated the charge-to-mass ratio to be...

• Average

[math]\displaystyle{ \frac{e}{m}=1.54\times10^{11}\frac{C}{kg} }[/math]

• SEM

[math]\displaystyle{ \frac{e}{m}=2.62\times10^{9}\frac{C}{kg} }[/math]

• Percent Error

[math]\displaystyle{ \% error=12.4%\,\! }[/math]

• Calculated ratio from the second graph

[math]\displaystyle{ \frac{e}{m}=\frac{2}{0.000002\times({7.8\times10^{-4}\times{1.324})}^{2}}\,\! }[/math]

[math]\displaystyle{ \simeq9.376\times10^{11}\frac{C}{kg}\,\! }[/math]

[math]\displaystyle{ \% error=\frac{R_{accepted}-R_{measured}}{R_{accepted}} }[/math]

[math]\displaystyle{ \% error\approx4.33%\,\! }[/math]

Conclusion

As mentioned in the discussion of our error in my lab notebook, I think that the biggest reason for our error was due to the difficulty reading the fixed ruler at the back of the apparatus to measure the radii of the electron beam. Overall, I was pretty satisfied with our results, I thought that we were going to have a larger error because of the difficulty reading the radius with the ruler. I would like to thank Katie for helping us with the circuit setup. If we were to do this lab again I would have tried to take more measurements to eliminate some of the error. Clearly one can see that there was more error from direct calculation than the error from the second graph in my lab notebook.