The electron beam Cathodes and anodes An electron gun usually consists of a cathode and an anode. The cathode is a filament that is connected to a potential difference (filament voltage), and the resulting current heats the filament to incandescence. Electrons boil off from the glowing surface of the cathode much like the filament in an ordinary light bulb. They then accelerate toward a positively charged electrode called the anode which had an opening through which some of the electrons pass. The result is a stream of the electrons whose kinetic energy is determined by the change in their electrical potential energy as they travel from the hot cathode toward the anode. If the potential difference between the cathode and anode is V (anode voltage), then the increase in the kinetic energy of the electrons is given by: ?K = e Vwhere e is the charge of the electron. Electrons leave the cathode with very little initial kinetic energy, so we can safely approximate ?K ~ K, where K is the kinetic energy of the electrons that reach the anode. Therefore, the kinetic energy of the electrons that go through the slit (at the anode) is: K = e VUse the expression above to write an equation for the speed of the electrons as a function of the anode voltage. This will be equation 1. Write this expression in the appropriate space at the beginning of activity 4 in the manual. What is the main source of kinetic energy of the electrons?