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HW 1.27

Posted: Thu Apr 19, 2018 10:48 am
by Joanna Pham - 2D
For question 1.27, we are asked to find the number of photons of violet light generated by a lamp in 2 seconds and how many moles of photons are emitted during those 2 seconds. It is given that the lamp is "rated at 32W emits violet light of a wavelength 420 nm."

I believe I am supposed to use E=(hc)/lambda, but since E stands for the energy of the photon, I am confused how to get the number of photons from this. Could someone please explain the process to me? Also, what is the 32W in this case? Is that just the energy of the light?

Re: HW 1.27

Posted: Thu Apr 19, 2018 2:16 pm
by Tiffany Chen 1A
32 W is the same as 32 J/s. Since you want to find the amount of photons generated after 2 seconds, multiply 32 J/s by 2 s (seconds cancel out) and then you're left with 64 J. 64 J is the total energy emitted (not sure if emitted is the right word) in 2 seconds. After using E=hc/lambda to find the energy per photon, I set up the equation (E per photon)(number of photons) = total E to find the number of photons. Then, I divided the number of photons by Avogadro's number to get the moles of photons.