The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall `3 m` away by means of a large convex lens. What is the maximum possible focal length of the lens required for the purpose ?

Options

A. `3.25` m
B. `1.55` m
C. `0.75` m
D. `0.28` m

Answer

C

Explanation

For a real image (on wall), the minimum distance between the object and image formed by the convex lens should be four times the focal length.
`:.` Maximum focal length of the convex lens is
`4f_("max")=3 m impliesf_("max")=(3)/(4) m=0.75 m`