Unit: Optics
Year: 1990 Question#: 94
Question:
If the mirror's radius of curvature could be increased, the focal length of the mirror would
(1 ) decrease
(2 ) increase
(3 ) remain the same
(4 )
What is this question really asking?
Explanation by: Frances J-P
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Answer 1
decrease
INCORRECT
The center is twice the focal length. Therefore if the distance from the center to the mirror was increased, the focal length would increase, not decrease.
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Answer 2
increase
CORRECT
A mirror's radius of curvature is directly related to its center length. The focal length is half the radius length, so if the radius of curvature is increased, the radius will increase in length also, therefore the focal length will increase.
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remains the same
INCORRECT
As explained in the diagram for answer 2, the focal length is directly proportional to the center length, which equal the radius of curvature. return to top
What's this question really asking?
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