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_(eq)) = (1)/(f_(1)) + (1)/(f_(2)) = (1)/(f) - (1)/(f) = 0 `
` f_(eq) = infty`.