The photoelectric effect demonstrates the particle nature of light in a clear way:
- Discrete energy transfer: Electrons are emitted when light shines on a material because they absorb energy from individual photons, not from the light wave as a continuous whole.
- Threshold frequency: Electrons are only emitted if the light’s frequency is above a certain value, regardless of its intensity. Classical wave theory predicted that increasing intensity should eventually release electrons, but experiments showed this doesn’t happen.
- Energy depends on frequency, not intensity: The kinetic energy of emitted electrons increases with the frequency of light, not its brightness. This implies that light energy comes in quanta (photons), each with energy proportional to its frequency.
- One-to-one interaction: Each photon interacts with a single electron. This one-to-one interaction is a hallmark of particle-like behavior, unlike waves, which distribute energy continuously.
Key idea: The photoelectric effect shows that light behaves as particles (photons) carrying quantized energy, providing strong evidence for the particle nature of light, which classical wave theory could not explain.