Inverse square law: Light bulb in wire frame.

Inverse square law: light bulb in wire frame. This demo is designed to show the inverse square law for light. That is, the intensity of light from a point source is proportional to 1/r , where r is the distance from the point source. The frame attached to the light bulb holder is built so that the distance to the first 6"x6" square is 1 foot, and the distance to the 1'x1' square is two feet. It is clear that the amount of light passing through the 6"x6" square spreads out to cover the 1'x1' square which is four times the area. Thus, the intensity of light at the 1'x1' square is 1/4 [or 1/(2x2)] that of the 6"x6" square. This can be tested by placing a silicon photocell at a distance of 1' and 2' from the lamp and measuring the amount of current.