A biconvex lens of focal length f forms a circular image of... | Physics | SolveeIt | Solveeit

Today, August 20

Question

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 convered by black sheet, then area of the image is equal to $\pi r^2/2$

D

If f is doubled, intensity will increase

Answer

$\pi r^2 \propto f^2$

Explanation

Solution

$\hspace25mm r=f \, tan \, \theta$
or $\hspace25mm r ? f \, \therefore \, \, \, \, \pi r^2 ? f^2$