(i) Find the de Broglie wavelength of electrons moving with a speed of `7xx10^(6)ms^(-1)`
(ii) Describe in brief what is observed when moving electrons are allowed to fall on a thin graphite film and the emergent beam fall on a fluorescent screen.

Explanation

(i) Since, `lambda=(h)/(p) ….(i)`
But, `p=mv ….(ii)`
Now, from equations (i) and (ii)
`implies lamda=(h)/(mv)=(6.6xx10^(-34))/(9.1xx10^(-31)xx7xx10^(6))m`
`lambda=1.03Åor0.103nm`
(ii) 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.
A beam of electrons is accelerated in an electron gun to a potential of between 3500 V and 5000 V and then allowed to fall on a very thin sheet of graphite. The electrons diffract from the carbon atoms and the resulting circular pattern on the screen is very good evidence for the wave nature of the electrons.

The different 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.