The photoelectric effect is one of the key experiments that helped establish the dual nature of light, showing that light behaves both as a wave and a particle. Here’s how:
- Wave behavior cannot explain it: Classical wave theory predicted that increasing the intensity of light should eventually release electrons, even at low frequencies. Experiments showed this does not happen—electrons are only emitted if the light’s frequency is above a threshold.
- Particle behavior explained it: Einstein proposed that light consists of photons, each carrying discrete energy proportional to its frequency. Each photon can knock out a single electron if its energy is sufficient, explaining why frequency, not intensity, determines electron emission.
- Evidence for duality:
- Light interferes and diffracts like a wave.
- Light interacts with electrons in discrete packets (photons) like a particle.
Key idea: The photoelectric effect shows that light cannot be described solely as a wave. Its behavior depends on the context: sometimes wave-like, sometimes particle-like—this is the essence of wave-particle duality in quantum physics.