Question

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 ?

Answer 1

Correct Answer - `0.75 m`
Here, distance between the object and image, `u + v = 3 m`
focal length of lens, `f = ?`
As maximum distance between an object and image in case of convex lens `= 4 f`,
`4 f = 3 m, f = 3/4 = 0.75 m`.