# Refractive index and focal length

When the refractive index of medium is greater than the lens then what will happen to the focal length of the lens?

The lens maker’s formula for a thin lens is: $$\dfrac{1}{f} = \left(\dfrac{\mu_2}{\mu_1} -1\right)\left(\dfrac{1}{R _1} - \dfrac{1}{R_2}\right)$$
Where $\mu_2$ is the refractive index of the lens, and $\mu_1$ is the refractive index of the medium.
If $\mu_1 > \mu_2$, then $\frac{\mu_2}{\mu_1} -1 < 0$.