# Photoelectric Effect ~ threshold frequency dependent on incident light?

 P: 3 1. The problem statement, all variables and given/known data True/False: In the photoelectric effect, the cut-off (threshold) frequency depends on the intensity of incident light. 2. Relevant equations hv = W + 1/2mv^2 v = W/h 3. The attempt at a solution The threshold frequency depends on the wavelength of incident light but not the intensity (??)
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P: 26,148
Hi ldesai149!
 Quote by ldesai149 … not the intensity (??)
That's right

the whole point of the experiment is that even if you reduce the intensity so that only one photon goes through at a time, that one photon still needs to have the threshold energy (or frequency)
 The threshold frequency depends on the wavelength of incident light …
no, the threshold frequency is fixed …

you might as well say "the threshold frequency depends on the frequency of incident light"

or "the minimum height for joining the army depends on the person's height"
 P: 60 I am a bit unclear on this process too. I never understood why an electron could not absorb the energy from several photons at the same instant and gain the required energy this way, rather than having to absorb from just a single photon at a time. Thanks :-)
 P: 70 Photoelectric Effect ~ threshold frequency dependent on incident light? one can't think about the photoelectric effect in terms of classical physics where the intensity of light is proportional to the square of the amplitude of the wave. In QM, one deals with light as individual packets of light. Imagine, one packet of light is able to interact with and excite one and only one electron. So, if it's energy ain't high enough (frequency below threshold freq) , it will not be able to eject the electron! However, increase in the intensity of light would just imply more number of incoming photons, and thus more electrons getting excited. ;)
Emeritus