Ray Optics: Practice Problem & Solution

Solution Explained:

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

Using the relation $f_l / f_a = (\mu_g - 1) / (\mu_g / \mu_l - 1)$, we substitute the given values: $f_l / 2 = (1.5 - 1) / (1.5 / 1.25 - 1)$.This simplifies to $f_l / 2 = 0.5 / (1.2 - 1) = 0.5 / 0.2 = 2.5$. Therefore, the focal length in liquid is $f_l = 2.5 \times 2 = 5 cm$.