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Unformatted text preview: s bulb with a small amount of helium gas inside. Physics 7B Charge-to-mass: e/m p. 5 When the gas molecules are struck by electrons they radiate a blue color, making the path of the electron beam—though not the electrons themselves—visible. Heater coils Anode (high voltage) Electrons + – Electron beam Cathode (low voltage)
Figure 1: A schematic drawing of the cathode-anode assembly, showing how the electron beam is generated from electrons boiled off of the cathode and accelerated towards the anode. The Magnetic Field To produce a uniform magnetic field, we place two large circular coils of wire known as Helmholtz coils around the tube, one on either side (see figure 2). The two coils have the same radius and the same number of turns (R = 0.15 meters and N = 130), and are placed exactly one radius R apart. When a current is passed through both coils in the same direction, the fields add to produce a very uniform magnetic field Btot in the center region between them. The field Btot is pointed along the line joining the centers of the two coils, and its magnitude at the center is related to the current in each coil by Eq. 2 above.
R Current I Current...
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