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Davisson-Germer experiment: proof of matter waves sheet
3-mark answer frame

Describe the experiment that first showed that electrons behave as waves.

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Name the experiment and its aim. Davisson-Germer experiment: to check whether electrons behave as waves.
  2. 2 · Describe the set-up. An electron gun (filament, accelerating voltage, slits) sends a fine beam onto a nickel crystal; a movable detector measures scattering at each angle; all in vacuum.
  3. 3 · Draw the apparatus. [Diagram: filament with L.T. battery, diaphragms with H.T. battery, electron beam, nickel crystal, scattered beam at θ to a movable detector, evacuated chamber]
  4. 4 · Give the result. For 54 eV electrons, a sharp peak at 50°, as for diffracted waves of λ ≈ 1.67 Å.
  5. 5 · Compare with theory. de Broglie's λ = 12.3/√54 ≈ 1.67 Å agrees.
  6. 6 · Close in one line. So, electrons are diffracted like waves: matter waves exist.

Scoring tip: State the numbers 54 V, 50° and 1.67 Å; they show the examiner you know the result.