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`
`:. (1)/(v)=(1)/(f)+(1)/(u) = (1)/(25)-(1)/(12.5)=(-1)/(25)`
`v = -25 cm`
As `m = (h_2)/(h_1) = (v)/(u) :. (h_2)/(5) = (-25)/(-12.5) = 2`
`h = 10 cm`.