Electron Gun Flashcards
(4 cards)
What is the definition of thermionic emission?
The emission of electrons through the action of heat.
Describe the process of thermionic emission.
A small metal filament is heated up by an electric current.
The electrons in this piece of wire gain Kinetic Energy.
Some of them gain enough Kinetic Energy to escape from the surface of the metal.
How does this relate to how an electron gun produces a narrow beam of electrons?
If the heated filament is placed in a vacuum and a high p.d. is applied between the filament and an anode, the filament would act as a cathode. Therefore the freed electrons accelerate towards the anode , gaining kinetic energy. If the anode has a small hole in it, then the electrons in line with the hole can pass through it which creates a narrow beam of electrons with a specific kinetic energy.
What sort of energy transfer is at play here?
As the electrons are accelerating they gain KE.
Therefore the work done on the electron is equal to KE.
eV=half m x v squared
This assumes that the electrons have negligible kinetic energy at the cathode.
