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Difference between "intensity of light" and "frequency of light"

Posted: Mon Oct 08, 2018 5:50 pm
by Sarah_Kang_2K
In the equation, E=hv where v = frequency, what is the difference between intensity and frequency of light?

In lecture, Professor Lavelle mentioned increasing the intensity of the light does not increase the energy of the individual photon. So, frequency and intensity can't refer to the same thing, right?

Re: Difference between "intensity of light" and "frequency of light"

Posted: Mon Oct 08, 2018 6:08 pm
by Fayez Kanj
Hey,

From what I understood, the frequency of light is how many cycles of the wave there are in 1 second (or per unit time). For example, if in 1 second, 10 waves pass, then the frequency is 10Hz (Hertz).

Also, the frequency of light is directly proportional to the energy of its photons ie: the higher the frequency, the higher the amount of energy in each photon. This is why the electrons were ejected from the metal surface when light with higher frequencies (shorter wavelengths) were used, such as UV light instead of visible light. Increasing the intensity will NOT change the energy of each photon, only how many photons there are, but if each photon individually doesn't have sufficient energy, then more photons will have no effect.

You could think of the intensity of light as the amplitude of the light wave. The bigger the amplitude, the more the intensity and vice versa. Light can be intense, but have a low frequency. Also, the more intense the light is, the brighter it is.


Hope this helps! :)

Re: Difference between "intensity of light" and "frequency of light"

Posted: Mon Oct 08, 2018 11:19 pm
by 904914909
That's a really great way to explain it, thanks for that clarification.

Re: Difference between "intensity of light" and "frequency of light"

Posted: Tue Oct 09, 2018 6:07 pm
by deepto_mizan1H
Thanks for the clarification up there, it is very helpful. I found this interesting because it helps to glean some insight on the importance of "quanta" in the particle model of light, where increasing the intensity of light will by no means change the energy in the photons. If it is already at a higher frequency, then the energy itself will correspond to whether the photons have enough energy to perform a change. It makes a very central principle of this form of mechanics very clear: the change in intensity will not be the same as on a larger scale (wave form) due to the importance of each photon's level of energy.