Question

A concave lens of refractive index 1.5 is immersed in a medium of refractive index 1.65. What is the nature of the lens?

Answer 1

if refractive index of medium is greater then refractive index of lens then lens gain opposite nature . e.g when lens is initially cancave then after submerge in medium lens show convex nature and voce-versa .
reason :-
we know ,
1/v. - 1/u. = (d - 1){ 1/ R 1 - 1/ R 2}
d is the relative refractive index of system.
if initially (d -1){ 1/R 1 - 1/R 2} is positive

after submerge ,
d=1.5/1.65 <1 so, ( d-1 ) < 0
it means
(d - 1){ 1/R 1 - 1/R 2 } will be negative .
so,
answer of this question ,
lens will be convex

Answer 2

Convex lens or converging lens.