The Photoelectric Effect: How Einstein Revolutionized Light

The photoelectric effect occurs when light shining on a metal surface ejects electrons.
Classical physics predicted light’s brightness should matter most—but it didn’t.
Einstein showed it’s light’s frequency, not intensity, that knocks electrons free.
This proved light comes in packets of energy called photons.
Higher-frequency light delivers more energy per photon to electrons.
The effect couldn’t be explained by wave theory alone, sparking the quantum revolution.
It provided direct evidence for light’s particle-like behavior.
Einstein’s 1905 paper on the effect won him the 1921 Nobel Prize in Physics.
The photoelectric effect laid the foundation for quantum mechanics.
Today, it powers technologies from solar panels to light sensors.