Electron diffraction

How is electron diffraction observed?

electrons accelerated in an electron gun and are focused through a gap similiar in size to their de broglie wavelength. Graphite film is ideal for this purpose due to its crystalline structure, gaps betweeen neighbouring planes of atoms act as slits. Circular pattern on a fluorescent screen made of phosphor observed.

How does the electron diffraction practical show electron difrraction?

If electrons acted as particles, no circular pattern would be observed, instead particles would be distributed uniformly across screen.

What does increasing the voltage between the cathode and the anode do?

causes the energy and hence speed of the electrons to increase. The kinetic energy is proportional to the voltage across the anode-cathode, Ek=eV

What is the equation for the de broglie wavelength?

λ=h/p or λ=h/mv

using Ek and momentum can be related by p= √(2mE) the de broglie wavelength can be written as λ= h/ √(2mE)

E= Ek of particle m= mass of particle

What does a larger radius of an electron diffraction pattern mean?

A low accelerating voltage/low Ek/momentum, longer wavelength, more diffraction.

What does a smaller radius of an electron diffraction pattern mean?

High accelerating voltage/high Ek/momentum, shorter wavelength, less diffraction.