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A lens having focal length f and apertur...

A lens having focal length f and aperture of diameter d forms an image of intensity 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 (I)/(4)`

B

`(3f)/(4) and (I)/(2)`

C

`f and (3I)/(4)`

D

`(f)/(4) and (I)/(2)`

Text Solution

Verified by Experts

The correct Answer is:
C
`f'=f`& Intensity `prop` Area so `I'=I -(I)/(4)=(3I)/(4)`
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