The pupil of the human eye is approximately 0.8 centimetres in diameter when adapted to the dark. What is the ratio of the light-gathering power of a 1.6 metre telescope to that of the human eye?
A) 2 : 1
B) 4 : 1
C) 200 : 1
D) 40,000 : 1

Question

Quizplus · Accepted Answer

The light-gathering power of a telescope compared to the human eye is proportional to the area of their apertures (diameters). The area of a circle is given by πr^2, so the ratio of their light-gathering powers is (1.6/0.008)^2 = (200)^2 = 40,000:1.

The Pupil of the Human Eye Is Approximately 0