Question

A double convex lens of glass of refractive index `1.6` has its both surfaces of equal radii of curvature of `30 cm `each. An object of height `5 cm` is placed at a distance of `12.5 cm` from the lens. Calculate the size of the image formed.

Answer 1

Correct Answer - `10 cm`
Here, `mu = 1.6, R_(1) = 30 cm, R_(2) = - 30 cm`
`h_(1) = 5 cm, u = - 12.5 cm, h_(2) = ?`
`(1)/(f) = (mu - 1)((1)/(R_(1)) - (1)/(R_(2)))`
`= (1.6 - 1)((1)/(30) + (1)/(30)) = (0.6)/(15)`
`f = (15)/(0.6) = 25 cm`
As `(1)/(v) - (1)/(u) = (1)/(f)`
`:. (1)/(v) = (1)/(f) + (1)/(u) = (1)/(25) - (1)/(12.5) = (-1)/(25)`
`v = - 25 cm`
As `m = (h_(2))/(h_(1)) = (v)/(a) :. (h_(2))/(5) = (- 25)/(-12.5) = 2`
`h = 10 cm`