Ray Optics and Optical Instruments Part 1

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
‌

1

f

=[1−1][‌

1

R1

−‌

1

R2

]=0
⇒‌‌‌

1

f

=0⇒f= Infinite