question_answer 62)

    Consider a thin target (10-2 m square, 10-3 m thickness) of sodium, which produces a photocurrent of 100  when a light of intensity  falls on it. Find the probability that a photoelectron is produced when a photon strikes a sodium atom. [Take density of Na = 0.97 kg/m3, Avogadro's number = 6 x 1026 kg atom],

Answer:

                      Volume of sodium target = A x d = 10-4 x 10-3 = 10-7 m3 We know that 6 x 1026 atoms of Na weighs = 23 kg    Volume of 6 x 106 Na atoms Volume occupied by one Na atom   No. of Na atoms in the target Let n be the number of photons falling per second on the target. Energy of each photon Total energy falling per sec on target    Let P be the probability of emission per atom per photon. The number of photoelectrons emitted per second As pr question, Current ,    Thus the probability of emission by a single photon on a single atom is very much less than 1. It is due to this reason, the absorption of two photons by an atom is negligible.