Question

Describe in brief what is observed when moving electrons are allowed to fall on a thin graphite film and the emergent beam falls on a fluorescent screen.

Answer 1

Electron diffraction is observed when moving electrons are allowed to fall on a thin graphite film and the emergent beam falls on a florescent screen. we can see it from diagram : A beam of electrons is accelerated in an electron gun to a potential of between $3500V$ and $5000V$ and then allowed to fall on a very thin sheet of graphite (see diagram above). The electrons diffract from the carbon atoms and the resulting circular pattern on the screen (see diagrams ) is very good evidence for the wave nature of the electrons.The diffraction pattern observed on the screen is a series of concentric rings. This is due to the regular spacing of the carbon atoms in different layers in the graphite. However since the graphite layers overlay each other in an irregular way the resulting diffraction pattern is circular. It is an example of Bragg scattering .