Bouncing Waves
In 1927, Davisson and Germer fired electrons at a nickel crystal and observed Diffraction—the same pattern you see when X-rays hit a crystal. Since diffraction is a wave property, this was the first experimental proof that de Broglie was right: electrons really are waves.
Worked Examples
Example 1: Bragg's Law
The peaks in the diffraction pattern follow Bragg's Law: \(n\lambda = 2d \sin \theta\). By measuring the angle \(\theta\) where the electrons bounced, they could calculate the wavelength \(\lambda\) and found it matched de Broglie's prediction perfectly.
The Bridge to Quantum Mechanics
Electron diffraction is the technology behind the Electron Microscope. Because electrons have much shorter wavelengths than visible light, they can resolve much smaller things (like atoms and viruses). This experiment proved that "wave nature" isn't a theory; it is a tool we use every day to see the subatomic world. If electrons were particles, your modern hard drive and your phone's processor couldn't have been designed.