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What is the average intensity at a distance?

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  1. Mar 4, 2015 #1
    1. The problem statement, all variables and given/known data
    A 60 W bulb radiates light uniformly in all directions. What is the average intensity of the light bulb at a distance 0.40 m.

    2. Relevant equations
    I = P/A, part of my problem is that I dont know the relevant equations

    3. The attempt at a solution
     
  2. jcsd
  3. Mar 4, 2015 #2
    Your equation is correct.
    You have to assume that the bulb radiates uniformly in all directions, then the area ##A## over which the power is distributed is the surface of a sphere with radius the distance you have.
     
  4. Mar 4, 2015 #3
    Thank you, that makes so much sense. I thought the area had to be of the object radiating the light.
     
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