Question

A microscope is focussed on an ink mark on the top of a table. lf we place a glass slab of 3 cm thick on it, how should the microscope be moved to focus the ink spot again? The refractive index of glass is 1.5

• A. 2 cm upwards
• B. 2 cm downwards
• C. 1 cm upwards
• D. 1 cm downwards

Answer 1

Answer: (C)

1 cm upwards

Answer 2

Given, $n = 1.5, h_\circ = 3\, cm$
Refractive index $n = \frac{h_\circ}{h_i}$
$1.5 = \frac{3}{h_i}$
$h_i = \frac{3}{1.5}= 2\, cm$
Hence, 3 - 2 = 1 cm upwards.