The intensity

The light intensity on a screen is inversely proportional to the square of the distance between the screen and the light source.

If a screen is illuminated by a light source 20 m away, the intensity is one-fifth of what is required. Where should the light be placed?

Correct answer:

x2 =  8.9443 m

Step-by-step explanation:

 I(x) = 1/x2  x1=20 m I1=1/5=51=0.2 I2=1   I   x2 =  K  K = I1   x12 = I2  x22 = const  K=I1 x12=0.2 202=80  x2=K/I2=80/1=4 58.9443 m   Verifying Solution:   I11=K/x12=80/202=51=0.2 I22=K/x22=80/8.94432=1

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