In a photoelectric effect experiment, there is no current flowing in the circuit.?

Question

Based on einstien's explanation of the photoelectric effect, why does increasing the intensity of the light source used in the experiment not cause the photoelectric effect to happen?

Answer 1

Well, if the frequency of the light source is high enough, turning on the light source would cause the photoelectric effect to happen. However, if the frequency of the light source is not high than a threshold frequency, increase the intensity of this light source will NOT cause the photoelectric effect to happen. This is because the energy of a photon is determined by its frequency. A higher intensity light source emits more photons than a lower intensity light source.
Are you questioning whether an atom absorb multiple photons and has a photoelectric effect? Oftentimes the condition can not be met, since it is very unlikely to have two or more photons to hit an atom at exactly the same time and same location. Besides, even if that very occasionally happen, the transition selectivity will be very different, and, the current of such effect may not be measurable today.

Answer 2

The photoelectric effect will not occur unless the light is of high enough energy - meaning the wavelength is short enough and the frequency is high enough. Red light has too long a wavelength and too low a frequency for the photoelectric effect to occur. It doesn't matter how intense the red light - it just is not strong enough to produce the effect.

Answer 3

There is a maximum energy that may be given to an ejected electron. this maximum is equal to the photon energy less the work function of the surface. Not all electrons have this amount of energy. Electrons may collide with other atoms or electrons and have lost some of their energy so they have less than this maximum, but none can have more. Now initially all the ejected electrons have sufficient energy to flow around the circuit with no opposing potential. But as you increase the opposing potential then some of the electrons do not have enough energy to flow. When you reach a potential equal to the maximum possible electron energy then the current falls to zero and remains at zero for all higher opposing potentials.