Refraction by Spherical Surfaces: Practice Problem & Solution

Solution Explained:

To solve this problem, we apply the core principles of Refraction by Spherical Surfaces. Understanding the underlying formula is key to arriving at the correct answer below:

The focal length of a lens in a liquid is given by $1/f_l = (\frac{\mu_g}{\mu_l} - 1)(\frac{1}{R_1} - \frac{1}{R_2})$. When the refractive indices are equal ( $\mu_l = \mu_g$ ), the term $(\frac{\mu_g}{\mu_l} - 1)$ becomes zero. This makes $1/f_l = 0$, meaning the focal length becomes infinite.