User:Chad A McCoy/Notebook/Jr. Lab/2008/10/27

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  • For this week's lab I am measuring the ratio e/m for the electron.
  • To do so I am using a Uchida e/m Experimental Apparatus, model TG-13, consisting of Helmholtz coils and an electron beam tube. Connected to the Helmholtz coils area Fluke 111 True RMS Multimeter and a SOAR Corporation Model PS-3600 DC Power Supply. Connected to the Defect Plates are a Amprobe 37XR-A True RMS Multimeter and a Gelman Instrument Company Deluxe Regulated Power Supply. Connected to the Electrodes for the electron gun, is the second output for the Gelman Power Supply. Lastly, connected to the heater for the electron gun are a second Amprobe 37XR-A multimeter and a SOAR Corporation 7403 DC Power Supply.
  • The purpose of the lab is to measure the radius of the deflected electron beam as a result of the magnetic field generated by the Helmholtz coils.
  • Connecting the supplies together and powering on the appparatus shows a horizontal beam from the electron gun, and after putting a current through the coils, we see a full circle once the current exceeds 1 Amp, and one that passes betweeen the wire leads when the current reaches 1.1 Amps.
Deflected Electron Ring from magnetic Current
Trial # Accelerating Voltage Coil Current Visual estimate
1 395.0V 1.622A 3.9cm 4.0cm
2 390.3V 1.802A 3.4cm 3.6cm
3 397.4V 1.417A 4.2cm 4.3cm
4 412.9V 1.332A 4.5cm 4.8cm
5 370.6V 1.328A 4.1cm 4.3cm
6 329.3V 1.478A 3.5cm 3.6cm
7 426.8V 1.839A 3.5cm 3.6cm
8 400.1V 1.303A 4.3cm 4.3cm
9 449.0V 1.304A 5.0cm 4.9cm
10 347.8V 1.306A 4.2cm 4.0cm
Fixed Voltage measurements
Trial # Accelerating Voltage Coil Current Visual estimate
1 400.0V 1.998A 3.1cm 4.0cm
2 400.0V 1.900A 3.2cm 4.1cm
3 400.0V 1.803A 4.1cm 3.5cm
4 400.0V 1.707A 3.6cm 4.3cm
5 400.0V 1.602A 4.0cm 4.5cm
6 400.0V 1.504A 4.5cm 4.4cm
7 400.0V 1.404A 4.5cm 4.7cm
8 400.0V 1.304A 4.7cm 5.0cm
Fixed Current measurements
Trial # Accelerating Voltage Coil Current Visual estimate
1 399.4V 1.500A 4.0cm 4.0cm
2 392.2V 1.500A 3.8cm 4.0cm
3 383.5V 1.500A 3.7cm 3.8cm
4 375.4V 1.500A 3.6cm 3.6cm
5 367.6V 1.500A 3.6cm 3.6cm
6 354.7V 1.500A 3.5cm 3.5cm
  • The data set for the constant voltage was taken with the heater voltage at 6.5V and the focus dial turned to its minimum value.
  • Because the data sets were requiring such a high accelerating voltage, I asked Dr. Koch about it, and we determined that the most likely reason was that the filament was dying. When Aram was also at my station, we experimented with changing the heater voltage and the focus, noticing that they changed the radius when altered.
  • Because of this, there is a great deal of systematic error as a result of the focus control, because rotating it changes the radius of the electron beam, without altering the accelerating voltage or current in the coils, such that it will allow for multiple distinguishable paths with no change to the calculations.