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

The correct option is A Shining bright red light on the surface

By the experimental study of photoelectric effects, we know that frequency (energy) of incident light on metal surface doesn't affect the photocurrent (no. of electrons emitting per second), only the frequency must be greater than threshold frequency for the emmision of electrons. Therefore in the given cases, change in the colour of light (change in frequency) will not affect , the no. of electrons emitting per second. Colour doesn't change the intensity of light in radiation theory, which is required to change the no. of electrons emitting per second but it is intensity of light (number of photons), on which number of electrons per second depends. When we change dim red light by bright red light, intensity is increased, hence the number of electrons ejected per second.