User:David J Weiss/Notebook/people/weiss/Rough Draft: Difference between revisions
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===Procedure and Methods=== | ===Procedure and Methods=== | ||
The general procedure can be found in Professor Gold's Lab Manual<small><sup>1</sup></small>. First of all you need to let the heater warm up for approximately 2 minutes, you do this by turning on the power, you can tell when this is warm because it will be glowing red. Once the heater is warmed up you apply a voltage of approximately 200V to the electron gun, you will start to see a beam of electrons this will glow green, if you | The general procedure can be found in Professor Gold's Lab Manual<small><sup>1</sup></small>. First of all you need to let the heater warm up for approximately 2 minutes, you do this by turning on the power, you can tell when this is warm because it will be glowing red. Once the heater is warmed up you apply a voltage of approximately 200V to the electron gun, you will start to see a beam of electrons this will glow green, if you don't see this you probably don't have it hooked up right. Once you see the electron beam you can now ally a current along the Helmholtz Coils, and when you do this you should see the electron beam start to take a circular orbit. Now you can start to take your data. The data you are going to collect is how big the radii of the electron is. There is a ruler set up on the other side of the e/m apparatus in which you can take your measurements. You will want to see how the beam is affected by changing the current along the coils while holding the voltage on the electron gun constant, and respectfully holding the current along the coils constant while fluctuating voltage. | ||
For my experiment I first started holding the current along the coils constant at 1.35A while fluctuating the voltage on the electron gun from a max value of 250V to a minimum voltage of 146V. I observed that the more voltage you apply while keeping the current constant the radius of the electron beam increases. For the next set of experiments I kept the voltage constant at 143V and had a range of current from 0.9A to 1.33A and observed that the radii increased as I decreased the current along the coils. I took data on the radii versus the current and radii versus the voltage and this can be found on my [[User:David_J_Weiss/Notebook/notes_E/m_Ratio|data page]] for this lab | |||
===Analysis Methods=== | ===Analysis Methods=== | ||
Revision as of 16:28, 15 November 2009
Determination of the Electrons mass versus its charge via experimentation
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 heater 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.
Procedure and Methods
The general procedure can be found in Professor Gold's Lab Manual1. First of all you need to let the heater warm up for approximately 2 minutes, you do this by turning on the power, you can tell when this is warm because it will be glowing red. Once the heater is warmed up you apply a voltage of approximately 200V to the electron gun, you will start to see a beam of electrons this will glow green, if you don't see this you probably don't have it hooked up right. Once you see the electron beam you can now ally a current along the Helmholtz Coils, and when you do this you should see the electron beam start to take a circular orbit. Now you can start to take your data. The data you are going to collect is how big the radii of the electron is. There is a ruler set up on the other side of the e/m apparatus in which you can take your measurements. You will want to see how the beam is affected by changing the current along the coils while holding the voltage on the electron gun constant, and respectfully holding the current along the coils constant while fluctuating voltage.
For my experiment I first started holding the current along the coils constant at 1.35A while fluctuating the voltage on the electron gun from a max value of 250V to a minimum voltage of 146V. I observed that the more voltage you apply while keeping the current constant the radius of the electron beam increases. For the next set of experiments I kept the voltage constant at 143V and had a range of current from 0.9A to 1.33A and observed that the radii increased as I decreased the current along the coils. I took data on the radii versus the current and radii versus the voltage and this can be found on my data page for this lab
Analysis Methods
Results and Discussion
dont think i need
Conclusion
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
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
