A convergent doublet of separated lens correct for spherical aberration, are separated by `2m` and has an equivalent focal lenth of `10cm`. Calculate the focal length of its component lenses.

Options

A. 18cm, 20cm
B. 10cm, 12cm
C. 12cm, 14cm
D. 16cm, 18cn

Answer

A

Explanation

For minimum spherical aberration separation,
`d=f_(1)-f_(2)=2cm`
Resultant length `=F=10cm`
Using `(1)/(F )=(1)/(f_(1))+(1)/(f_(2))-(d)/(f_(1)f_(2))` and solving, we get `f_(1), f_(2)` 18 cm and 20 cm respectively.