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Homework Help: A few light problems?

  1. Mar 18, 2005 #1
    1) Find the illumination 4.2 m below a 415 lm lamp.

    2) A screen is placed between two lamps so that they illuminate the screen equally. The first lamp emits a luminous flux of 1445 lm and is 2.7 m from the screen. What is the distance of the second lamp from the screen if the luminous flux is 2350 lm?

    3) Two lamps illuminate a screen equally. The first lamp has an intensity of 101 cd and is 4 m from the screen. The second lamp is 5 m from the screen. What is the intensity of the second lamp?


    These should be very easy. However, I'm doing this for a friend and I don't have his book or any of the formulas. Help me out?
  2. jcsd
  3. Mar 18, 2005 #2
    Intensity is proportional to the inverse square of radius.

    I = L / R^2, this should help you solve all three of hte above questions, since they are basically the same.
  4. Mar 19, 2005 #3
    I = L / R^2
    i = 415/4.2^2
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