A microscope is focussed on a3 mark on a piece of paper and then a slab of glass of thickness 3 cm and refractive index 1.5 is placed over a mark. How should the microscope be moved to get the mark again in focus?

Question

A microscope is focussed on a3 mark on a piece of paper and then a slab of glass of thickness 3 cm and refractive index 1.5 is placed over a mark. How should the microscope be moved to get the mark again in focus? (A) 1 cm upward (B) 4.5 cm downward (C) 1 cm downward (D) 2 cm upward

Tardigrade Admin · Accepted Answer

Apparent depth of mark as seen through a glass slab of thickness

x

and refractive index

μ

is

Apparent depth = \frac{Real depth}{Refractive index}

or

x = \frac{x}{μ} = \frac{3}{1.5} = 2 c m

As image appears to be raised by 1 cm, therefore, microscope must be moved upwards by 1 cm.

Q. A microscope is focussed on a3 mark on a piece of paper and then a slab of glass of thickness 3 cm and refractive index 1.5 is placed over a mark. How should the microscope be moved to get the mark again in focus?

1 cm upward

4.5 cm downward

1 cm downward

2 cm upward

Apparent depth of mark as seen through a glass slab of thickness x and refractive index μ is Apparentdepth=RefractiveindexRealdepth​ or x=μx​=1.53​=2cm As image appears to be raised by 1 cm, therefore, microscope must be moved upwards by 1 cm.

Apparent depth of mark as seen through a glass slab of thickness $x$ and refractive index $μ$ is
$Apparent depth = \frac{Real depth}{Refractive index}$
or $x = \frac{x}{μ} = \frac{3}{1.5} = 2 c m$
As image appears to be raised by 1 cm, therefore, microscope must be moved upwards by 1 cm.