The intensity of light measured in foot-candles varies inversely with the square of the distance from the light source.

Question

Suppose the intensity of a light bulb is 0.02 foot-candles at a distance of 3 meters. Find the intensity level, I, at 8 meters.

Answer 1

I = k/d^2

k = Id^2 = (.02)3^2 = 9(.02) = .18

I = .18/d^2

at a distance of 8 meters Intensity = .18/(8)^2 = .18/64

= 0.0028125 foot candles