Refraction by Plane Surfaces: Practice Problem & Solution
A microscope is focused on a mark on a piece of paper and then a slab of glass of thickness $3 cm$ and refractive index $1.5$ is placed over the mark. How should the microscope be moved to get the mark in focus again? (2006)
Solution Explained:
To solve this problem, we apply the core principles of Refraction by Plane Surfaces. Understanding the underlying formula is key to arriving at the correct answer below:
When a glass slab is placed over a mark, the mark appears raised by a distance known as normal shift.
Normal shift $\Delta t = t(1 - \frac{1}{\mu}) = 3(1 - \frac{1}{1.5}) = 3(1 - \frac{2}{3}) = 1 cm$.
To focus again on the apparent image, the microscope must be moved $1 cm$ upward.
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