Physics-
General
Easy

Question

The distance between a point source of light and a screen which is 60 cm is increased to 180 cm. The intensity on the screen as compared with the original intensity will be

  1. (1/9) times    
  2. (1/3) times    
  3. 3 times    
  4. 9 times    

The correct answer is: (1/9) times


    I proportional to fraction numerator 1 over denominator r to the power of 2 end exponent end fraction rightwards double arrow fraction numerator I subscript 2 end subscript over denominator I subscript 1 end subscript end fraction equals fraction numerator r subscript 1 end subscript superscript 2 end superscript over denominator r subscript 2 end subscript superscript 2 end superscript end fraction equals fraction numerator 6 0 to the power of 2 end exponent over denominator 18 0 to the power of 2 end exponent end fraction equals fraction numerator 1 over denominator 9 end fraction

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