Question

A lens having focal length f and aperture of diameter d forms an image of intensity I. Aperture of diameter d/2 in the central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively:

• A. \(f,\; \dfrac{I}{4}\)
• B. \(\dfrac{3f}{4},\; I\)
• C. \(f,\; \dfrac{3I}{4}\)
• D. (f)/(2), (I)/(2)

Hint:

• Aperture affects intensity • Focal length depends only on lens geometry

Answer 1

The Correct Option is C