Q.State the importance of Davisson and Germer experiment.

[!TLDR] The Davisson-Germer experiment was the first DIRECT experimental proof that matter has wave-like character, by showing electrons scattered from a nickel crystal produce a genuine diffraction pattern whose measured wavelength matched de Broglie's theoretical prediction closely -- turning de Broglie's hypothesis into an experimentally verified physical law. …

The importance of the Davisson and Germer experiment lies in what it PROVED, not merely what it observed. Before 1927, de Broglie's proposal that matter possesses an associated wavelength $\lambda=h/p$ was a purely theoretical hypothesis, based on an elegant but unproven argument from symmetry between waves and particles -- it had no direct experimental support.\n\nDavisson and Germer scattered a beam of electrons, accelerated to a known energy, off the regularly spaced atoms of a nickel crystal, and found that the scattered electron INTENSITY was not smooth or featureless (as a purely classical-particle picture would predict) but showed sharp peaks and troughs as a function of scattering angle -- a genuine DIFFRACTION pattern, exactly the signature phenomenon that only WAVES can produce (through constructive and destructive interference). This was decisive: only a wave, not a classical particle, can diffract.\n\nCrucially, the wavelength worked out independently from the geometry of this observed diffraction pattern (about 0.165 nm, at the 54 V, 50° peak) matched closely with the wavelength de Broglie's own formula, $\lambda=1.228/\sqrt{V}$ nm, predicted for that same 54 V accelerating potential (about 0.167 nm) -- purely from a theoretical relation originally derived by analogy with photons, with no reference to the crystal experiment at all. This close numerical agreement between an independent theoretical prediction and an independent experimental measurement is exactly the kind of evidence that turns a hypothesis into an established physical law.\n\nThe experiment therefore did three i …

Explain that the experiment's importance is providing the first direct EXPERIMENTAL confirmation (via observed electron diffraction) of what had until then been only a theoretical hyp …

Describing only WHAT the experiment did (scattered electrons off nickel, observed a diffraction peak) without explaining WHY that mattered -- namely, that it was the first direct proof that mat …