Wave-Particle Duality

Two years after de Broglie came up with his particle wavelengths and idea that electrons could diffract, Davisson and Germer proved this to happen.

They fired electrons into a crystal structure which acted as a diffraction grating. This produced areas of electrons and no electrons on the screen behind it, just like the pattern you get when light diffracts.

Electron Wavelength

We can calculate the de Broglie wavelength of an electron from the potential difference, V, that accelerated it.

Change in electric potential energy gained = eV

Sand Analogy

If we compare a double slit electron diffraction to sand falling from containers we can see how crazy electron diffraction is. Imagine two holes about 30cm apart that sand is dropping from. We would expect to find a maximum amount of sand under each hole, right? This is not what we find! We find a maximum in between the two holes. The electrons are acting like a wave.

Wave-Particle Duality

Wave-particle duality means that waves sometimes behave like particles and particles sometimes behave like waves. Some examples of these are shown below:

Light as a Wave

Diffraction, interference, polarisation and refraction all prove that light is a wave and will be covered in Unit 2.

Light as a Particle

We have seen that the photoelectric effect shows that light can behave as a particle called a photon.

Electron as a Particle

The deflection by an electromagnetic field and collisions with other particles show its particle nature.

Electron as a Wave

Electron diffraction proves that a particle can show wave behaviour              .