Question

Intensity of Light. The intensity I of light from a light bulb varies inversely as the square of the distance d from the bulb. Suppose that I is
90
W
/
m
2
90W/m2 (watts per square meter) when the distance is 5 m. How much farther would it be to a point where the intensity is
40
W
/
m
2
40W/m2?

Answer 1

I = k/d^2
so, Id^2 = k is constant

So, find d such that

40d^2 = 90*5^2

and subtract 5