Question

Suppose you are enjoying a warm summer afternoon at the local swimming pool, when you see your old chemistry teacher across the water. Foolishly, he has left the strawberry daiquiri he was drinking sitting near the edge of the pool.

a) Should the wave you initiate to knock over his drink have a large wavelength, frequency, or amplitude?

b) If, on the other hand, you were trying to “knock over” an electron using a laser beam, would you choose light waves of large wavelength, frequency, or amplitude? Why the difference

c) What does this have to do with the photoelectric effect?

Answer 1

a] The wave you would initiate must have a large amplitude for it to reach the drink and knock it.

b] To 'knock over' and electron is to remove an electron from the lattice structure it is in. This would require some threshold energy [work function] and this energy is given through photons in this case. For a photon, its energy is proportional to its frequency [E = hf] and so you would choose large frequency and not amplitude in this case.

c] This threshold energy is the work function of a metal and it is minimum energy required to eject an electron from the metal lattice. It is not dependent upon electric field amplitude of the incident wave but rather on the frequency of the wave. If an energy greater than this threshold energy is provided, the remaining energy is just imparted to electrons as their kinetic energy.