A light source at a distance of 1 meter that emits 50 watts of visible radiation has the same _____________ as a source emitting 200 watts and is located ____________.
A) luminosity; 2 meters away
B) luminosity; 4 meters away
C) apparent brightness; 2 meters away
D) apparent brightness; 4 meters away

Question

Quizplus · Accepted Answer

Apparent brightness decreases with the square of the distance. A 200-watt source at 2 meters has the same apparent brightness as a 50-watt source at 1 meter because (200 watts)/(2^2) = (50 watts)/(1^2).

A Light Source at a Distance of 1 Meter That