At a small distance r from a long cylindrical light source, the intensity produced is proportional to

Step-by-step solution

Intensity of light is defined as the power transmitted per unit area. For a long cylindrical light source of length L , the light spreads out uniformly over a cylindrical surface of radius r coaxial with the source. The surface area of this imaginary cylinder is A = 2 r L . If P is the power emitted by the cylindrical source of length L , the intensity I at a distance r is given by: I = P A = P 2 r L Since P and L are constant for a given source, we obtain: I 1 r