Question

A thin glass (refractive index 1.5) lens has optical power of -5D in air. It’s optical power in a liquid
medium with refractive index 1.6 will be

(A) 25D (B) -25D
(C) 1D (D) None of these

PLEASE EXPLAIN ALSO.

Answer 1

NONE OF THESE AS BY SOLVING IT WE GET ANSWER AS O.5D

Answer 2

Correct option is (D) None of these

P=(u2/u1 - 1) (1/R1 - 1/R2)

-5= (1.5/1 - 1) ( 1/R1-1/R2)

-5/0.5 = 1/R1 - 1/R2

or 1/R1 - 1/R2 = -10

Taking P=(1.5/1.6 - 1) (-10)

= (-0.1) (-10)/1.6

=5/8 D