Question

A coin is kept at bottom of an empty beaker. A travelling microscope is focused on the coin from top, now water is poured in beaker up to a height of 10 cm. By what distance and in which direction should the microscope be moved to bring the coin again in focus

• A. 10 cm up ward
• B. 10 cm down ward
• C. 2.5 cm up wards
• D. 2.5 cm down wards

Answer 1

Answer: (C)

2.5 cm up wards

Answer 2

When water is poured in the beaker. Coin appears to shift by a distance $\mathbf{d =}\frac{\mathbf{h}}{\mathbf{4}}\mathbf{=}\frac{\mathbf{10}}{\mathbf{4}}\mathbf{= 2.5cm}$

Hence to bring the coil again in focus, the microscope should be moved by 2.5 cm in upward direction.