Suppose the distance between an observer and a lightbulb is doubled. How does its final brightness compare with its initial brightness?
A) The lightbulb appears 1/16 as bright.
B) The lightbulb appears 4 times brighter.
C) The lightbulb appears 1/2 as bright.
D) The lightbulb appears 1/4 as bright.

Question

Quizplus · Accepted Answer

The brightness of a light source follows the inverse square law, meaning that if the distance between the observer and the light source is doubled, the brightness appears 1/4 as bright because the light spreads out over four times the area.

Suppose the Distance Between an Observer and a Lightbulb Is