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### Photons in a light source

Posted: Sat Apr 14, 2018 11:03 am
Assuming you had some light source, are all of the photons in that light source of the same energy level? The formula E = hv makes me think the answer would be yes but in lecture, one of the slides said "low frequency light has no photons with efficient energy" which makes me think some light sources could have, for instance, half with the correct energy level and half without.

### Re: Photons in a light source

Posted: Sat Apr 14, 2018 1:39 pm
I reviewed my notes and cannot find where that was said. are you sure it said photons? you could be mistaking that for electrons. if so no electrons are ejected if the energy of the photon is not greater than or equal to the work function aka the energy needed to eject an electron. so back to the statement "low-frequency light has not photons with efficient energy" if you replace photons with electrons in the statement (which I think is correct) it makes more sense because for the eq E=hv ... if you lower the frequency the energy level also decreases... which can cause no electrons to be emitted.

### Re: Photons in a light source

Posted: Sat Apr 14, 2018 1:45 pm
E=hv calculates the amount of energy per photon of a light source with that particular frequency, so all photons of that light source would have the same amount of energy. I think the "low frequency light has no photons with sufficient energy" from lecture is referring to the 1 to 1 photon-electron interaction that has to happen in order to eject an electron from a metal surface (each photon has to have enough energy to remove 1 electron). So, if the frequency of the light source is too low, then the energy of each photon is too low to remove an electron. Therefore, none of the photons of that light source would have enough energy to remove any electrons, no matter how many photons you have.

### Re: Photons in a light source

Posted: Sat Apr 14, 2018 3:38 pm
tatianatumbling_1J wrote:I reviewed my notes and cannot find where that was said. are you sure it said photons? you could be mistaking that for electrons. if so no electrons are ejected if the energy of the photon is not greater than or equal to the work function aka the energy needed to eject an electron. so back to the statement "low-frequency light has not photons with efficient energy" if you replace photons with electrons in the statement (which I think is correct) it makes more sense because for the eq E=hv ... if you lower the frequency the energy level also decreases... which can cause no electrons to be emitted.

I think it did say photons because we are talking about a light source. I think I understand now from what Tiffany said. Remember the particles in light are referred to as photons so I don't think it would make sense to talk about the electrons in comparison to the threshold energy.

### Re: Photons in a light source  [ENDORSED]

Posted: Mon Apr 16, 2018 3:10 pm
If you have a light source of a given wavelength, all of the photons emitted by that light source will have the same energy.