## Intensity in terms of Quantum Mechanics and Classical Mechanics

$c=\lambda v$

Steven Luong 1E
Posts: 33
Joined: Fri Apr 06, 2018 11:03 am

### Intensity in terms of Quantum Mechanics and Classical Mechanics

Hi everyone,

Professor Lavelle mentioned both intensity of light in terms of quantum mechanics and classical mechanics. I was not so sure how both of these are different from one another. Can somebody elaborate on their differences?

annie_finneran_1K
Posts: 37
Joined: Fri Apr 06, 2018 11:02 am

### Re: Intensity in terms of Quantum Mechanics and Classical Mechanics

I believe in classical mechanics, the intensity of a wave is based on amplitude, or height of the wave. In quantum mechanics, and with light, the intensity of the wave is not correlated to amplitude, but rather by the frequency/wavelength of each photon. In the photoelectric effect, it is not the number of photons, but the strength/frequency/wavelength (intensity) of each photon that determines if the electron is ejected. Anyone else want to elaborate?

Sam Metzger 1C
Posts: 25
Joined: Wed Apr 04, 2018 3:00 am

### Re: Intensity in terms of Quantum Mechanics and Classical Mechanics

Right, the classical model is shown by the physical wave (like in the ocean for example) with the intensity determined by amplitude. The taller the wave, the greater the intensity. Then with the photon model in quantum mechanics, the intensity of the photon is determined by the amount of them. Then in the photoelectric effect, intensity does not determine if an electron can be ejected from a sheet of metal. What determines it is simply the frequency of the photon. Shorter frequencies carry greater energy and are able to remove an electron. Then, with more of these photons present, more electrons can be removed, hence there is a 1:1 ratio of photons to electrons.