> ANSWER 20 INTENSITY OF ILLUMINATION The intensity of illumination I from a source of light varies inversely as the square of the distance d from the source. (a) Express I in terms of d and a constant of variation k. (b) A searchlight has an intensity of 1,000,000 candlepower at a distance of 50 feet. Find the value of k in part (a). (c) Sketch a graph of the relationship between I and d for d > 0. (d) Approximate the intensity of the searchlight in part (b) at a distance of 1 mile.