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Homework Help: Photons per second from lightbulb

  1. Mar 31, 2015 #1
    1. The problem statement, all variables and given/known data

    If 5 percent of the power of a 100 W bulb is radiated in the visible spectrum, how many visible photons are radiated per second?

    2. Relevant equations


    3. The attempt at a solution

    I know how to solve this, I just wanted to make sure.
    I will take 5 W or J/s as the power of the visible light, and once you know the energy of the visible light's photon in Joules finding the photons/second is easy. I am wondering though if it would be better to present a range of photons per second since the visible spectrum is a range of frequencies/wavelengths, or an average. The question seems like it wants a single answer.
  2. jcsd
  3. Mar 31, 2015 #2
  4. Mar 31, 2015 #3


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    Staff Emeritus
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    Surely you could find a range. Then pick some reasonable answer in the middle.

    You might assume white light - so an even distribution of frequencies, The energy is proportional to the frequency, so you get a nice energy distribution. Integrate over that someway.

    Want to make things even more complicated? - - -
  5. Mar 31, 2015 #4
    Haha that's alright. I found a range as well as the average and will list those both, hopefully that is a satisfactory answer.
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