Question

| (a) Einstein's interpretation of the photoclectric effect was important in the early development of quantum mechanics. It indicated a departure from the wave model of light, and required energy to be quantised. Consider the following experimental parameters: maximum kinetic energy of emitted electrons, intensity of light, frequency of light, number of emitted electrons, delay time for electrons to be emitted. In termš of some of these parameters, briefly discuss TWO observations in the photoelectric effect experiments that cannot be understood using the wave model of light, and how they were interpreted by Einstein's quantised model. (i) Einstein's interpretation led to the following relationship Emax hv-W Give a brief definition and/or explanation of each of the variables in this equation. (ii)

Answer 1

1- (1) There is no emission of photo-electron below a certain minimum frequency regardless the intensity of the intensity of incident radiation.this frequency known as threshold frequency and depends upon nature of emitting surface.

(2) At fixed frequency, the number of ejected electron increase with the intensity of the light but does not depend on its frequency.

Einstein's hypothesis

Energy in light is concentrated in small packets know as photons. The incident photon transfer whole energy to one electron without time lag. A certain minimum energy called work function is required to eject the electron.

2- Emax =hv - W

Emax= maximum energy of emitted electron

hv= energy of photon

W= work function of surface

The maximum energy of emitted electron is energy of incident photon subtract by the work function of surface.