m lab - also record the accelerating voltage. Next align...

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Kevin Chou 5/24/2010 e/m Apparatus lab Introduction The purpose of the lab is to calculate and measure the e/m: the charge to mass ratio. By using the PASCO Model SE-9638 e/m apparatus, the e/m can be measured. A beam of electron is accelerated through the e/m tube. By measuring the accelerating potential (V), the current to the Hemlholtz coils (I), and the radius of the electron beam (r) e/m can be calculated with the equation: e/m=2V/B 2 r 2 . Procedure The apparatus must have the following adjustment to the electron gun. Heater must be at 6.3 VAC or VDC. Electrodes are at 150 to 300 VDC. The Helmholtz coils are set to 6-9 VDC. When the experiment begins, slowly turn the knob for the Helmholtz coils clockwise, but the current must not exceed 2A. An electron beam will be accelerated through the e/m tube. Record the current to the Helmholtz coils, and
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Unformatted text preview: also record the accelerating voltage. Next align the electron beam with its reflection to measure the radius of the electron beam. Data Current to Helmholtz coils (I)= 1.44A Accelerating voltage (V)= 183.6 Electron beam radius (r)= 4 Calculations The equation used to find the e/m: e/m=v/Br=2V(5/4) 2 a 2 /(N Ir) 2 N is the number of loop in the coils: 130 a is 15cm it is the radius of the Helmholtz coils. V=183.6 I= 1.44 r= 4 e/m= 1.822 x 10-11 The actual number would be 1.766 x 10-11 Percent of error |1.766 x 10-11-1.822 x 10-11 |/1.766 x 10-11 x 100% Percent of error is 3.17% Analysis The source of error may be due to the imperfection of the apparatus. The machine itself may not be exactly accurate. Also, when measuring the radius, it was a rough estimate as it was difficult to obtain the exact number....
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This note was uploaded on 11/18/2010 for the course ACC 2002 taught by Professor Staff during the Spring '08 term at UChicago.

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m lab - also record the accelerating voltage. Next align...

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