Question

A microscope is focus on an ink mark. A glass plate is placed over the mark. In order to focus the

mark, the microscope is to be raised 1 mm. In order to focus on upper surface of the glass plate, it

must be raised 2 mm further. Find the refractive index of glass​

Answer 1

Answer:

Answer is 1.5.

ExplanationThe slab is 3 mm thick because, it lifts the image 1mm up and to reach its top, we need to lift the microscope 2 mm further. So, 1mm +2 mm = 3mm.

#Assumption 1--Suppose if we take the real depth as 5 mm, so we will see the image 1mm up, i.e. at 4mm. And to focus on the dot, we will have to raise the microscope at 4mm. According to the question, to focus on the top of the slab, the microscope is raised 2 mm further. But in this assumption (that the glass slab is of 5mm) we will have to raise the microscope 3mm more.

#Assumption 2--But when the thickness is 3mm, then to focus the dot, we need to raise the microscope 1 mm further, i.e. we will focus at 2mm. And now we are already at 2mm. So to focus on the top of slab, we need to raise it 2 mm further. This is how the thickness of the slab is 3mm.

In this answer, the distance of the slab to microscope has not been given. So it has been neglected.

Hope this helps.