1 more math question!?

Question

This time, it's:
The intensity of light from a source is inversely proportional to the square of distance from the source. a) Express this relationship in an equation. b) If the intensity is 4 watts at 6 meters from the source, find the intensity 8 meters from the source.

Thank you!

Answer 1

a) Let the intensity at a distance r be given by I(r). Then the equation is I(r) = k/r^2.

b) I(8) = I(6).(6/8)^2 = 4.(3/4)^2 = 9/4 = 2.25 watts.