A beam of red light and a beam of violet light each deliver the same power on a surface.For which beam is the number of photons hitting the surface per second the greatest?
A) the red beam
B) the violet beam
C) It is the same for both beams.

Question

Quizplus · Accepted Answer

The energy of a photon is given by $E = hf$, where $h$ is Planck's constant and $f$ is the frequency of the light. Since violet light has a higher frequency than red light, each photon of violet light carries more energy. Therefore, for two beams delivering the same power, the beam with the lower energy photons (red light) must have a greater number of photons hitting the surface per second.

A Beam of Red Light and a Beam of Violet