A biconvex lens of focal length f forms a circular image of radius r of sun in focal plane . Then which option is correct

Options

A. `pir^(2)propf`
B. `pir^(2)propf^(2)`
C. If lower half part is covered by black sheet, then area of the image is equal to `pir^(2)//2`
D. if `f` is doubled, intensitywill increase

Answer

B

Explanation

`r=f tanalpha`

Hence, `pir^(2)propf^(2)`