Davisson-germer Experiment

The Davisson-Germer experiment directed a collimated beam of electrons, accelerated through a known potential, onto a nickel crystal and measured the scattered intensity as a function of angle. A pronounced maximum appeared at a specific scattering angle, exactly mimicking the constructive interference produced when waves diffract from the regularly spaced atomic planes of a crystal. The angular position matched the de Broglie wavelength $\lambda =\frac{12.27}{\sqrt{V}}\text{A˚}$ predicted for the electrons, providing direct quantitative confirmation that electrons propagate as waves. The option about electron spin is unrelated, as spin was established through magnetic experiments such as Stern-Gerlach. Nuclear-charge quantisation belongs to scattering work by Rutherford and Moseley, not this experiment. The particle nature of light is demonstrated by the photoelectric and Compton effects, the conceptual converse of this matter-wave result. By verifying de Broglie's hypothesis with electrons, this experiment completed the symmetry of wave-particle duality, a centrepiece of the NCERT dual-nature chapter. The internal consistency between the measured diffraction angle and the calculated wavelength is what makes the conclusion compelling. A noteworthy detail is that the experiment originally succeeded almost by accident, after the nickel target was recrystallised into large single domains following an oven mishap, which sharpened the diffraction maxima dramatically. This historical twist underscores how the regular atomic spacing of a crystal acts as a natural diffraction grating perfectly suited to the angstrom-scale wavelengths of slow electrons.