Einstein is rightly famed for his revolutionary work on relativity. But he was also one of the founders of quantum physics and in 1905 became the first physicist to apply Max Planck's quantum hypothesis to light. Einstein realized that the quantum picture can be used to describe the photoelectric effect – that only light above a certain frequency can eject electrons from the surface of a metal.Indeed, it was mainly for deriving the law of the photoelectric effect that he was awarded the 1921 Nobel Prize for Physics.