Question

Select One Correct Option from the following: A biconvex lens of focal length f forms a circular image of radius r of sun in focal plane. Then which option is correct?
(A) $\pi r^{2} \propto f$.
(B) $\pi r^{2} \propto f^{2}$.
(C) If lower half part is covered by black sheet, then area of the image is equal to $\pi r^{2} /2$.
(D) If f is doubled, intensity will increase.

Answer 1

a option is correct.
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