TBR: Light Color v. Intensity

[justadream]

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TBR Physics Book II page 245



The example talks about polychromatic light and lists light with its intensity as follows:



Blue: 10

Green: 3

Red: 7



Isn’t intensity related to energy? And energy is related to frequency. So how is red light more intense than is green light?

 

[Cawolf]

I am pretty sure that passage is talking about the intensity of the light in that specific experiment. It isn't saying that a purely red light is more intense than purely green light.

The intensity is used to determine which spike on the graph in the choices is which wavelength. It is strictly for this passage.

 

[milski]

Intensity and energy are related but are not the same thing. The wave length determines the energy of a single photon but not of the whole beam. If you have more photons with the same energy, you'll have a beam with higher energy and the same wavelength/color.

The intensity tells you how many photons are in the beam (per second), so the higher it is, the more photons you have. You cannot directly compare the energy of two beams just from their intensity - one of them can have less photons but higher total energy, if the wavelength is low enough.