Consider a convex lens of refractive index µ2 and µ1 is the refractive index of the medium in which it is placed.
⇒µ2=µ1.....(i) According to the lens Maker's formula,
1
f
=[
µ1
µ2
−1][
1
R1
−
1
R2
]....(ii) where, f is the focal length of the lens, R1 and R2 are the radii of curvature of respective faces of lens. From Eqs. (i) and (ii), we can write