measurement of em

measurement of em - Laboratory Report PHYS 122L The...

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Laboratory Report PHYS 122L The Measurement of e/m for the Electron Purpose of the Experiment: To utilize the force produced by a magnetic field acting on a moving charge, in order to measure the ratio of the charge of an electron to its mass, i.e. e/m. Experimental Procedure: A set of Helmholtz coils are used to produce a relatively uniform magnetic field that is used to deflect a beam of electrons that can be viewed on a luminescent screen coating a mica sheet. The electrons are accelerated by a cathode ray gun, composed of a tungsten filament, which is the source of the electrons, and an anode which accelerates the electrons into the tube. The voltage from the high voltage power supply is adjusted until a visible electron beam appears. The current through the Helmholtz coils is increased until the electron beam straightens out. This value is recorded as I o . The accelerating voltage is then set to 2,000 volts and the current in the Helmholtz coil is varied until the electron beam strikes point A on the mica screen. The magnitude of the current is recorded as I; cycle the current up and back down and “hit” point A at least four times, allowing us to compute an uncertainty in I. Repeat this procedure for the other four points so that you have five different values of current for this particular voltage. The voltage is increased by 500 volts and the above procedure is repeated; repeat this process until you reach an
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measurement of em - Laboratory Report PHYS 122L The...

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