User:David J Weiss/Notebook/people/weiss/Rough Draft

Determination of the Electrons mass versus its charge via experimentation

Author: David Weiss Experimentalists: David Weiss, Elizabeth Allen University of New Mexico, Department of Physics and Astronomy MSC07 4220, 800 Yale Blvd NE, Albuquerque, New Mexico 87131-0001 USA Contact info: dweiss01@unm.edu

Abstract

The ratio for electric charge to the mass of an electron is a fundamental concept in physics and a good experiment to be conducted by persons interested in a study of physics. With this result you can determine how much charge an electron has in relation to its mass. From this you can conclude how the electron is affected by gravity and by the electric field. To find this we use a procedure that is outlined in Professor Gold's Laboratory Manual¹. This can be done with an electron gun a Helmholtz Coil and a couple of power sources. With all these things we can determine how a beam of electrons curves within a magnetic field and thus measure a radius and with some tricky manipulation figure the ratio for electric charge compared to mass for the electrons. Based upon my calculations I found that the electric charge versus the mass for an electron is approximately 2.3(.23)*10^11 coul/kg and this was off by about 30.68% and considering that the main measurement for the radii was taken by reading a ruler on the back of the electron gun I think that it is a good result.

Introduction

The charge of an electron is one of the most basic concepts in the entire study of electromagnetism and atomic particles. The charge to mass ratio was first shown by J.J. Thompson in his famous experiment². Its actual charge was later found by R.A Millikan³. This can be found by studying the effects of an electric and magnetic field on charged particles.

The first person o find an electron was J.J. Thompson. He did so in a series of experiments which used cathode ray tubes to try to find electrons. He did three such different experiments and it wasn't until the third that he found the charge to mass ratio for the electron which he found in 1987. These results let him to formulate his "Plum Pudding Model" of the atom. This experiment is a lot like the one detailed here. For these experiments he was awarded the Nobel Prize in Physics in the year 1906.

After Thompson did these experiments R.A. Millikan came around and found through experimentation the charge of the electron. His experiments which involve dropping oil droplets in a chamber that could be charged to see how the oil droplets reacted in an electric field. These experiments then lead to the charge that an electron has on it. He was later awarded the Nobel Prize in Physics for these experiments in 1923 after some controversy due to the deeds of one Felix Ehrenhaft's claim that he found a smaller charge than Millikan, but these claims turned out to be wrong and the prize was given to Millikan.

With out these fundamental experiments we could have not found the charge of the electron, and with out this fundamental constant we could not have been able to do some of the work in chemistry atomic physics and quantum mechanics. The experiment that i did was similar to the experiment that Thompson did in that I am using an electron gun to "boil" off electrons and measure how they behave in a magnetic field. I will vary the force of the electrons by mean of changing the voltage to the electron gun which is the Lorenz Force⁴, I will also vary the magnetic field by means of changing the current that is applied to the Helmholtz Coils⁵ to show how an electron responds to a changing electric field and or a changing force.

Experiment and Materials

Set Up

An electron gun is housed in a bulb that has some gas in to so you can see the electron beam. There is also a Helmholtz Coil attached to this apparatus so that a uniform magnetic field can be generated. This is one manufactured piece so you don't have to worry about aligning everything properly which make it nice(e/m Experimental Apparatus Model TG-13 Uchida Yoko). Once you get this peace you need three different power supplies each one connects to a different part of the e/m apparatus. You need to connect a 6-9 Vdc 2A power supply (SOAR corporation DC Power Supply Model 7403, 0-36V, 3A)to the Helmholtz Coil with a multimeter in series (BK PRECISION Digital Multimeter Model 2831B). Then connect a 6.3V power supply (Hewlett-Packard DC Power Supply Model 6384A)to the electron gun jacks. Finally connect a power source rated at 150-300V (Gelman Instrument Company Deluxe Regulated Power Supply) with another multimeter (BK PRECISION Digital Multimeter (Model 2831B) to the electron gun.

e/m Experimental Apparatus (Model TG-13)

(bottom) Hewlett-Packard DC Power Supply (Model 6384A, 4-5.5V, 0-8A) and (top) BK PRECISION Digital Multimeter Model 2831B

(left of e/m E. A.) SOAR corporation DC Power Supply Model 7403, (top right) BK PRECISION Digital Multimeter Model 2831B, (bottom right) Gelman Instrument Company Deluxe Regulated Power Supply

Procedure and Methods

The general procedure can be found in Professor Gold's Lab Manual¹

Results and Discussion

dont think i need

Acknowledgments

I would like to thank my lab partner Elizabeth Allen, my lab professor Dr.Steven Koch our lab TA Pranav Rathi for all your assistance and support during this lab.

References

1.Professor Golds Lab Manual

2.[Paper by J.J. Thompson]

3.[Paper by R.A. Millikan] R. A. Millikan, "On the elementary electrical charge and the Avogadro constant". The Physical Review, Series II 2: 109–143 (1913).

4.Lorenz Force

5.Helmholtz Coil