Which two main observations in photo electricity led Einstein to suggest the photon theory for the interaction of light with the free electrons in a metal? Obtain an expression for the threshold frequency for photoelectric emission in terms of the work function of the metal. [CBSE SQR 2011]
Two main observations :(i) The maximum kinetic energy of the emitted photo electrons is independent of the intensity of light. (ii) For each photo emitter, there exists a threshold frequency (of incident light) below which no emission takes place.