A spherical convex surface separates object and image space of refractive index `1.0 and 4/3.` If radius of curvature of the surface is `10cm,` find its power.

Options

A. 3.4D
B. 2.5D
C. 25D
D. 1.5D

Answer

b.

Explanation

Let us see where does the parallel rays converge or diverge on the principal axis. Let us call it the focus and the corresponding length the focal length f. Using
`(mu_(1))/(v)-(mu_(2))/(u)=(mu_(2)-mu_(1))/(R)`
With proper values and signs, we have
`(4//3)/(f)-(1.0)/(oo)=(4//2-1.0)/(+10)`
or `f=40cm =0.4m`
Since the rays are converging, its power should be positive.
Hence,
P(in dioptre) `=(+1)/(f("meter"))=(1)/(0.4)`
or `P=2.5D`