The electric current and voltages are measured with two digital multimeters: the Triplett Multimeter Model 4000 and Simpson Digital Multimeter Model 464. This supply also provides the cathode heater power using a 6.3-V alternating current. A voltage of 150 – 300 V at a modest current of approximately 50 mA is required. The accelerating voltage for the EBB is produced by a Heathkit Regulated Power Supply Model PS-4. The apparatus is fed by three external power sources. There is also an illuminated ruler behind the EBB to facilitate the measurement of the electron-beam radius. The centerpiece of this experiment is the Kent \(e/m\) Experimental Apparatus Model TG-13, which consists of the electron-beam bulb (EBB) and a pair of Helmholtz coils (HC). If there is no electric field, then this relation can be written as The electron's equation of motion is given by the Lorentz relation. The trajectory of the speeding electrons moving through the magnetic field is made visible by a small amount of mercury vapor.Īn electron moving in a uniform magnetic field travels in a helical path around the field lines.
A known current flows through a pair of Helmholtz coils and produces a magnetic field. The central piece of this apparatus is an evacuated electron-beam bulb with a special anode. An electron beam of a specified energy, and therefore a specified speed, may be produced conveniently in an \(e/m\) apparatus. Fortunately, the ratio of these two fundamental constants can be determined easily and precisely from the radius of curvature of an electron beam traveling in a known magnetic field. Measuring separately the electric charge (\(e\)) and the rest mass (\(m\)) of an electron is a difficult task because both quantities are extremely small (\(e\) = 1.60217733×10 -19 coulombs, \(m\) = 9.1093897×10 -31 kilograms). Heathkit Regulated Power Supply Model PS-4.GW Laboratory DC Power Supply Model GPS-1850.Kent \(e/m\) Experimental Apparatus Model TG-13.
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