The Determination of The Charge to Mass Ratio of the Electron
A magnetic field produced by Helmholtz coils is used to deflect electrons into circular paths whose radii are known. By knowing the energy of the electrons and the magnetic field strength, the ratio of the charge to mass of the electron (e/m) is determined.
A tube designed specifically to determine the charge to mass ratio of the electron is used in this experiment. This e/m tube consists of an electron gun composed of a straight filament surrounded by a coaxial cylindrical anode containing a single axial slit. The beam of electrons is produced by this gun. (Refer to Figure 1.)The various parts in Figure are labeled as follows:
A) five crossbars attached to a stiff wire
B) a typical path of the beam of electrons
C) the cylindrical anode
D) the distance from the filament to the far side of the crossbar
E) the lead wire and support for anode
F) the filament
G) the lead wires and support forthe filament
Figure I (a) A top view of the e/m tube.
(b) A crossectional view of
the filament assembly.
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