Which has the larger light-gathering power
A)a telescope of 5 cm diameter and focal length of 50 cm
B)a telescope of 6 cm diameter and focal length of 100 cm
C)a telescope of 2 cm diameter and focal length of 100 cm
D)a telescope of 3 cm diameter and focal length of 75 cm
E)both b and c since they have the same focal length.

Question

Quizplus · Accepted Answer

The light-gathering power of a telescope is proportional to the area of the objective lens or mirror. This can be calculated using the formula A = pi*(D/2)^2, where A is the area and D is the diameter. Therefore, the area of telescope B is greater than A, C, and D. The focal length does not affect light-gathering power, so choice E is incorrect.

Which Has the Larger Light-Gathering Power