Compared with the 2.5-m-diameter Mount Wilson telescope,the 10-m-diameter Keck telescope has a greater light-gathering power by a factor of:
A) 4.
B) 16.
C) 2.
D) 1; they have the same light-gathering capability.

Question

Quizplus · Accepted Answer

The light-gathering power of a telescope is directly proportional to the area of its primary mirror. The area of a circle is proportional to the square of its diameter. Therefore, increasing the diameter by a factor of 4 (from 2.5 m to 10 m) increases the light-gathering power by a factor of 16 (4^2). So, the Keck telescope has 16 times greater light-gathering power than the Mount Wilson telescope.