Question

d u momentum of the emitted photon. 7. [15-22) (a) [5] How many photons are there is 1 J of light at a wavelength of X-500 nm? (b) [5] Why is there a cutoff frequency for electromagnetic radiation below which electrons are not emitted from a metal. (b) [5-12] Explain how it is that Einstein's explanation of the photoelectric effect is in conflict with basic notions of classical physics and how it is that this explanation leads to totally new physical picture of light and matter. 7 points of extra credit will be awarded for a fuller answer.

Answer 1

E = nho E = nhe number of photons n= . nc ne 1x 500 x 169 6.63x1034x 3 x 18 17 n= 25.14X10 6 It frequency of incident light is less than cutoff (threshold) frequency vo energy of photon ho will be less than Work function of metal and hence electron cannot come out of metal b (5-12) Einstien explained photo-electric effect on basis of quantum theory accoding to which me photos incident on metal can make only me electhen to emit from metal surface How large way be the energy of incident photon this is in conflict with Classical Physics which allows emission of more than an electron when photos has more energy.