The Inverse Square Law

  • Thread starter emtis
  • Start date
  • #1
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Homework Statement


Problem One: Two kilometres away from a point source of infrared waves, the intensity is 4 Mw−2. Calculate the intensity 1m away from the source.

Problem two: Light from a candle has an intensity of 20.0 units when a meter is placed 3.0m away. What is the reading on the light meter when it is brought to 1.0 m away?


Homework Equations


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The Attempt at a Solution


Yeah, about that. I'm not really sure where to start. I mean, I have the answers with me, and I think I am able to fill in the values for the inverse square law, but I don't know how to manipulate the equation with fractions to get the answer that I want. I always struggle here, because I ****ing hate fractions and I can't seem to get one thing write with them. I'd like to see the solution with respect to the given formula above please.
 

Answers and Replies

  • #2
tms
644
17
Look at the first problem. You are given the intensity and distance for one measurement; let those be ##I_1## and ##d_1## respectively. You are also given another distance, and you want to find the intensity at that spot; let those be ##d_2## and ##I_2##. You have to solve the equation you have above for ##I_2##, and then plug in the numbers you have to get your answer.
 
  • #3
1,948
200
If your problem is with fractions than I think you should go back to basics and solve many more fraction problems from some introductory text that includes lots of examples and exercises.
 

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