How does the power supply affect electron emission at the cathode filament?

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Multiple Choice

How does the power supply affect electron emission at the cathode filament?

The main concept is thermionic emission: the number of electrons emitted from the cathode filament depends on how hot the filament is. The power supply provides current to the filament, turning electrical energy into heat. As the filament temperature rises, more electrons gain enough energy to overcome the metal’s work function and be emitted from the surface. This emission increases with temperature in a non-linear but strong way, described by the thermionic emission relationship J ≈ A T^2 e^{-φ/(kT)}. So, by controlling the filament current (and thus its temperature) the power supply directly controls how many electrons are emitted. Other choices don’t fit because the power supply’s role here is not to accelerate electrons toward the anode, nor to set the energy of emitted photons, nor to cool the filament. Acceleration toward the anode is achieved by high voltage after emission, photon energy depends on different factors, and cooling would reduce emission rather than drive it.

The main concept is thermionic emission: the number of electrons emitted from the cathode filament depends on how hot the filament is. The power supply provides current to the filament, turning electrical energy into heat. As the filament temperature rises, more electrons gain enough energy to overcome the metal’s work function and be emitted from the surface. This emission increases with temperature in a non-linear but strong way, described by the thermionic emission relationship J ≈ A T^2 e^{-φ/(kT)}. So, by controlling the filament current (and thus its temperature) the power supply directly controls how many electrons are emitted.

Other choices don’t fit because the power supply’s role here is not to accelerate electrons toward the anode, nor to set the energy of emitted photons, nor to cool the filament. Acceleration toward the anode is achieved by high voltage after emission, photon energy depends on different factors, and cooling would reduce emission rather than drive it.

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