There is an equiconvex glass lens with radius of each face as R and and . If there is water in object space and air in image space, then the focal length is
(a) 2R (b) R
(c) 3 R/2 (d)
(c) Consider the refraction of the first surface i.e. refraction from rarer medium to denser medium
Now consider the refraction at the second surface of the lens i.e. refraction from denser medium to rarer medium
The image will be formed at a distance of . This is equal to the focal length of the lens.