Question

An object of height `1cm` is set at angles to the optical axis of a double convex lens of optical power `5D` and `25cm` away from the lens. Determine the focal length of the lens, the position of the image. The linear magnification of the lens, and the height of the image formed by it.

Answer 1

Correct Answer - `20cm, 1m, -4, 4cm`
`P = 5D rArr f = (1)/(5)m = 20cm`
By lens formula
`(1)/(f) = (1)/(v) - (1)/(u), (1)/(20) = (1)/(v) - (1)/(-25)`
`rArr (1)/(v) = (1)/(20) - (1)/(25)`
`rArr (1)/(v) = (5)/(20xx25) rArr v = 100cm = 1m`
`m, = (h_(2))/(h_(1)) = + (v)/(u) = (100)/(-25) = -4 rArr h_(2) = -4cm`