The Electron Diffraction Experiment

The electron diffraction experiment clearly shows the wave properties of electrons. In order for diffraction to take place, an electron wave must pass through a gap of about the same order as the wavelength of the electron. The atomic spacing in crystal is such a gap. If a beam of electrons is incident on a crystal then diffraction will take place. The experimental arrangement is shown below.

Electrons from an electron source are accelerated though a voltage V and pass through a crystal lattice, undergoing diffraction here. The diffraction pattern is displayed on a screen.

If the accelerating voltage is 1000 V, then the electrons will gain kinetic energy equal to

We can find the speed of the electrons using (for non relativistic speeds)

The de Broglie relationship then gives the wavelength of the electrons:

The electron waves will display constructive interference in certain directions and destructive interference in others.

If the crystal is rotated, circles will form.

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