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### How many photons

Posted: Fri Oct 19, 2018 6:13 pm
Hi,
Problem 1B.9 on the homework says:
A lamp rated at 32 W emits violet light of wavelength 420 nm. How many photons of violet light can the lamp generate in 2.0 s?
Can someone please explain how to find the number of photons of light that can be generated?
Thank you

### Re: How many photons

Posted: Fri Oct 19, 2018 6:30 pm
First you have to calculate the energy from the lamp, which is simply 32J/s *2s = 64J (1 W = 1 J/s). Next you are given the wavelength of the light that the lamp emits. You can calculate the energy corresponding to that wavelength (using E=hc/wavelength), which would give the the energy PER PHOTON of light. Once you have that, you can divide 64J by your answer which is in J/photon to give you the # of photons.

### Re: How many photons

Posted: Fri Oct 19, 2018 7:29 pm
To answer the second part of the question of 1B9 "How many moles of photons are emitted in that time interval?" you would multiply your number of photons from the first question and multiply that by (1mol/(6.022 x 10^23 photons) to cancel out the photons and get the moles produced of photons.

### Re: How many photons

Posted: Tue Oct 23, 2018 3:25 pm
Thank you!