A beam of parallel rays is brought to focus by a planoconvex lens. A thin Concave lens of the same focal length is joined to the first lens. The effect of this is

Options

A. the focal point shifts away from the lens by a small distance
B. the focus remains undisturbed
C. the focus shifts to infinity
D. the focal point shifts towards the lens by a small distance.

Answer

C

Explanation

`(1)/(F)=(1)/(f)+(1)/(-f)=0impliesF=infty`