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Homework Help: Number of photons emitted from a light bulb entering the eye

  1. Dec 6, 2009 #1
    1. The problem statement, all variables and given/known data

    A 100W bulb emits light of a single wavelength 6000*10^-10 m. If light spreads out uniformly in space, how many photons enter your eye per second if you are at a distance 1m from the bulb and the pupil diameter is about 1mm?

    2. Relevant equations

    E = hc/lambda

    3. The attempt at a solution

    I found the energy of each photon using E =hc/lambda and i know i have to divide the proportion of light entering the eye by this to find the number of photons entering the eye. I also know that the proportion of light entering the eye is area of pupil/ area of sphere. the area of sphere is 4*pi*r^2 = 4*pi*1 but what is the area of the pupil?
  2. jcsd
  3. Dec 6, 2009 #2


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    Homework Helper

    The pupil is a circle. What's the formula for area of a circle?
  4. Dec 6, 2009 #3
    i assumed it would've been harder to find.
    thanks so much!
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