The photoelectric effect is a phenomenon in which light shining on a metal surface ejects electrons from that surface. Although light was once thought to behave purely as a wave, this effect showed that light also exhibits particle-like behavior—a key piece of evidence for the development of quantum theory.
Einstein’s Contribution:
In 1905, Albert Einstein explained the photoelectric effect by proposing that light is made of discrete packets of energy called photons. He suggested that:
- Each photon carries energy proportional to its frequency.
- If a photon has enough energy, it can knock an electron out of a metal atom.
- Increasing the intensity of light doesn’t eject more energetic electrons unless the frequency (and thus the energy of the photons) is high enough.
This explanation went against classical wave theory, which couldn’t account for the fact that no electrons were emitted below a certain light frequency, regardless of the intensity.
Why It Was Revolutionary:
- It provided direct evidence that light behaves as both a wave and a particle (wave-particle duality).
- It helped lay the foundation for quantum mechanics.
- It resolved a major mystery in physics at the time regarding how energy is transferred by light.
Nobel Prize Recognition:
Einstein received the Nobel Prize in Physics in 1921 not for his theory of relativity, but for his groundbreaking explanation of the photoelectric effect, which fundamentally changed our understanding of light and energy.