The Photoelectric Effect; Quanta and Photons
Why light behaves as a stream of energy packets when it strikes matter
Big Idea: When light shines on a metal it can knock electrons out of the surface. This is the photoelectric effect. Careful experiments show it cannot be explained if light is only a smooth wave. Light behaves as a stream of tiny energy packets called photons, each carrying energy E = hf. A single photon gives all of its energy to a single electron. This idea, from Planck and Einstein, opened the door to all of quantum physics.
By the end you will be able to:
- describe how light interacts with matter and ejects electrons,
- state the three experimental laws of the photoelectric effect,
- use the photon energy formula E = hf = hc/λ,
- apply Einstein's photoelectric equation hf = A + Ek,max,
- explain the work function and the red boundary (threshold frequency),
- describe photocells and where they are used.