A lens having focal length 
and aperture of diameter 
forms an image of intensity 
Aperture of diameter 
in central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively
A
and 
B
and 
C
and 
D
and 
Text Solution
Verified by ExpertsThe correct answer is:
C
: Focal length of the lens remains same. Intensity ofimage formed by lens is proportional to area exposed to incident light from object. i . e ., Intensity 
area
or 
Initial area, 
After blocking, exposed area,
or 
Hence, focal length of a lens 
, intensity of the image 
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