Physics307L F08:People/Le/e/m

--Linh N Le 22:34, 28 October 2007 (CDT)

Purpose/Procedure
The purpose of this lab is to measure the ratio of the charge of an electron (e) to its mass.

We will send a beam of charged electrons perpendicularly through a magnetic field. The field will produce a force on the beam, bending it into a circle. By measuring the radius of the circle, we will be able to calculate the ratio of e/m.

For a more comprehensive look into this lab, I refer you to my notebook: F08:People/Le/Notebook/071008 Part 1 F08:People/Le/Notebook/071015 Part 2

Data
I will forgo the tedium of reporting all my measurements (as that can be found in the lab) and get right to the meat of the problem.

4 sets of data were taken, and the respective e/m ratios are:


 * 3.2116e11 +/- 6.3934e09 C/kg
 * 3.2246e11 +/- 7.7978e09 C/kg
 * 4.5411e11 +/- 1.2047e10 C/kg
 * 2.7461e11 +/- 8.7489e08 C/kg

The accepted value is: 1.76e11 C/kg

Errors
Comparing the values we got to the accepted values, I'm able to give relative % errors

%error set 1=82.5%

%error set 2=83.2%

%error set 3=158%

%error set 4=56.03%

Final Thoughts
The data is precise, but very inaccurate. I would have to say that the apparatus has fundamental design flaws, although it itself if constructed properly.

The way of measuring the radius involves a high amount of error, since we must account for paralax.

Increasing the voltages supplied to the apparatus increases the accuracy of the data, but that has a cap before we overload the apparatus.