Physicopoeia

φυσικοποιΐα
THINGS I WISH I'D KNOWN WHEN I STARTED TEACHING PHYSICS

Electron Diffraction: take readings to confirm λ = h/p

Many syllabuses include the de Broglie relationship which claims that any particle with momentum can behave as a wave (λ = h/p). Yet many textbooks and courses do not give pupils any decent empirical evidence that this relationship is actually accurate. If you have the apparatus to show electron diffraction through graphite, you can show that electrons can in fact behave like waves and form a diffraction pattern.

Very few sources, however, take this one step further and take readings from the apparatus which confirms the de Broglie relationship. In fact, if de Broglie is correct, the diameter of a given diffraction ring should be inversely proportional to the square root of the electron's accelerating PD. This sheet goes through the derivation of this relationship and has a results table for pupils to fill in: