Electron Diffraction

Brook Edgar

Teacher

Explainer Video

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Electron Diffraction

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Practice Question

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Brook Edgar

Head of Physics

Explainer Video

Electron Diffraction

We have already learned that light can behave as a particle from the PEE or as a wave from Young's double slit experiment. This is known as wave-particle duality.

Electrons can also behave as particles or waves. We already know that they are particles as they can ionise atoms and can be deflected in magnetic and electric fields. We know that electrons can behave as waves, as they can be diffracted, producing an interference effect similar to that of light waves.

5.4

A beam of electrons fired at the same velocity towards a thin layer of atoms is diffracted through the atoms, much like light through a double slit, producing an interference pattern of bright and dark rings on the screen.

The wavelength of the electrons is known as the de Broglie wavelength:

Formula:

Worked Example

What will happen to the diffraction rings if the speed of the electrons is increased?

Answer:

As fringe width decreases, the diffraction rings will become closer together.

Worked Example

Calculate the wavelength of an electron moving at . State your answer in .

A narrow beam of these electrons is directed at a metal foil, which has a few rows of atoms separated by . Explain what is observed on the screen behind the foil.

Calculate the voltage required to accelerate an electron to .

Answers:

An interference pattern of bright and dark fringes will be observed on the screen. This is due to constructive and destructive interference as the electrons diffract through the gaps in the atoms as the de Broglie wavelength of the electrons and the atom separations are on the same order of magnitude.

The pd needed to accelerate the electrons to this speed can be found by equating the kinetic energy of the electrons to the energy gained by the electrons on moving through a pd, .