A lens having focal length f and aperture of diameter d forms an image of intensity I. Aperture of diameter d/2 in central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively
A
f and 
B
and 
C
f and 
D
and 
Text Solution
Verified by ExpertsThe correct answer is:
C
By covering the aperture of diameter d/2, focal length of lens is not affected. Area reduces by 
th. So does the intensity.
New focal length = f, and
New intensity 
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