# Explain how the Davisson–Germer experiment provided evidence for the wave nature of electrons.

> IB DP Physics Higher Level (2023 syllabus) — E.2 Quantum physics (HL only) · Explain · 4 marks

> In 1927, Davisson and Germer directed a beam of electrons at a nickel crystal and detected a strong reflected intensity at specific angles. The pattern they observed was consistent with that expected from wave interference.

## Mark scheme (4 marks)

1. Electrons were reflected from the nickel crystal and produced a diffraction (interference) pattern with intensity maxima at specific angles.
2. Such a diffraction pattern can only arise if the electrons behave as waves, with adjacent atomic planes in the crystal acting as a diffraction grating (similar to X-ray diffraction).
3. The de Broglie wavelength of the electrons (λ = h/p) matched the wavelength calculated from the angular positions of the diffraction maxima using the Bragg condition / constructive interference condition.
4. This confirmed de Broglie's hypothesis that matter (particles with mass) possesses wave-like properties and demonstrated wave–particle duality for electrons.

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