Question

When I shine dim red light on a metal surface, some electrons are ejected. Which of the following would not significantly increase the number of electrons per second being ejected from the surface?
A. Shining bright red light on the surface
B. Shining bright white light on the surface
C. Shining dam (higher energy) purple light on the surface
D. shining bright (higher energy) green light on the surface
E. All of the previous actions would increase the number of electrons per second being ejected from the surface.

Answer 1

Hint : In the question, we have a question that is from the concept of photoelectric effect. We have to recall the experimental observation and related important points to make a conclusion here. From the given options, we could concentrate on the intensity, frequency and also energy of incident light.

Complete step-by-step solution:
In the question, we are told that on shining dim red light on a metal surface, electrons are ejected. We are given some options below it and we have to find the correct one among them.
We could find the answer from the experimental study of photoelectric effect.
The frequency of incident light has nothing to do with the number of electrons emitted per second and hence the photocurrent. It is only required for the incident light’s frequency to be greater than the threshold frequency for the electronic emission.
It is the intensity of the incident light on which the number of electrons emitted depends. Therefore, on shining the red light brighter, the intensity is increased so will the number of electrons emitted per second.
Hence, option A is found to be correct.

Note: Basically, there would be a certain threshold frequency that would be required for the electronic emission to take place. We have already said that the red light does cause electronic emission and therefore the threshold frequency is there for the incident light. That is why we have concentrated on the intensity.