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.
b
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