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Candelas and distance

  1. May 12, 2009 #1
    1. The problem statement, all variables and given/known data
    A 10-cd point source lamp and a 70-cd point source lamp cast equal intensities on a wall. If the 10-cd lamp is 8.0 m from the wall, how far from the wall is the 70-cd lamp?



    2. Relevant equations
    I'm not sure what the equation for a candela is.


    3. The attempt at a solution
    Can't attempt it without knowing an equation.


    That's the only information given, and I don't know how to form an equation.
     
  2. jcsd
  3. May 12, 2009 #2
    A candela is a unit of intensity for light. And you remember that intensity falls off as 1/r^2.
     
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