Question

Converging lens of refractive index 1.5 is kept in a liquid medium having the same refractive index what would be the focal length of the lens in this medium?

Answer 1

Infinite, because

\(\frac{1}{f} = (\frac{\mu_2}{\mu_1 } -1)(\frac{1}{R_1} - \frac{1}{R_2})\)

= \((1 -1) (\frac{1}{R_1} - \frac{1}{R_2}) = 0\)

∴ f = ∞