The photoelectric effect is a phenomenon in which light shining on a metal surface causes electrons to be ejected from that surface. This effect played a crucial role in confirming that light is made of particles called photons, and that these photons carry momentum and energy.
What Happens in the Photoelectric Effect:
- When light of a certain frequency hits a metal, it can transfer energy to electrons.
- If the energy is high enough, the electrons absorb this energy and are released from the metal.
- This only occurs if the light has a frequency above a certain threshold—regardless of how intense the light is.
Why It Matters:
- This discovery challenged the classical wave theory of light, which predicted that increasing the brightness of light should increase energy transfer, but experiments showed this wasn’t the case.
- Albert Einstein explained this effect by proposing that light comes in discrete packets of energy (photons).
- Each photon has energy related to its frequency, and when it strikes an electron, it transfers that energy directly.
- This also implies that photons carry momentum, even though they have no mass.
Impact on Physics:
- The photoelectric effect provided solid evidence for quantum theory.
- It demonstrated that light behaves both as a wave and as a particle (wave-particle duality).
- Einstein received the Nobel Prize in Physics in 1921 for his explanation of the photoelectric effect.