← Unit 7: Quantum, Atomic, and Nuclear Physics
The Photoelectric Effect
Light striking a metal can eject electrons, but only if individual photons carry enough energy — a key piece of evidence for light's particle nature.
Overview
Photon energy E = hf (Planck's constant times frequency). The photoelectric effect shows that increasing light INTENSITY doesn't help eject electrons if the frequency is too low — only increasing frequency (photon energy) does, contradicting a purely wave-based picture of light.
Practice Quiz
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Dim, high-frequency light ejects electrons from a metal, but very bright, low-frequency light does not. What does this demonstrate?