User:Jared A. Booth/Notebook/Physics 307L/2009/10/28

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e/m Ratio


  1. To measure the ratio of the charge versus mass on an electron.



Uchida e/m Experimental Apparatus Model TG-13
Two BK Precision Digital Multimeters, Model 2831B
Gelman Instrument Company Deluxe Regulated Power Supply
SOAR Corporation DC Power Supply Model 7403
HP DC Power Supply Model 6384A


Personal Safety: In this lab we will be dealing with high voltage currents as well as currents of up to 2 amperes. Currents as low as 100 mA can be lethal (Wikipedia) so proper caution is essential.

Equipment Safety: The power supply for the heating element should not exceed 6.3V. Ensure all equipment is undamaged and hooked up properly before applying any currents. A not pasted to the top of one of the digital multimeters indicates it is possibly broken, signed Steve Koch and dated January, 2009.


The procedure will be followed according to the lab manual

Day 1

We began by inspecting all equipment for damage before we connected it.

Day 2

We began by ensuring all the equipment was still hooked up properly and set correctly. We then turned on the heater power supply to 6.7V and let it heat for approximately 10 minutes. We then turned on the accelerating voltage to 300V. We turned on the current to the coils and attempted to bend the electron beam in a circle so that it passed between the two wires near the heater. The beam's radius was too large to fit within the bulb, so the voltage was reduced to 255V. The current was set to -1.31A and measurements were made and compared to the measurements for these values from day 1. The measurements seemed to be significantly different, 5.4cmL/4.1cmR versus 5.1cmL/4.3cmR from before. Upon inspecting the focus, it was found that adjustments changed the radius of the circle as well as turn the beam to create a helix. The focus was adjusted and the bulb mount turned such that measurements for this current and accelerating voltage were similar to those from day 1.
The current was reduced from -1.31A until the beam was cut off by the bulb at -1.22A. The voltage was lowered to 200V to reduce the radius and allow a larger range of currents to be measured. The new range was -1.32V to -1.06V. Measurements were then taken in increments of 0.02A. The voltage was then reduced to 188V and more measurements were taken in increments of .02A from -1.31A to -1.05A.

Raw Data

Data Analysis

Error Analysis