Question

An experiment is performed to find the refractive index of glass using a travelling microscope. In this experiment distances are measured by:
(A) A meter scale provided on the microscope
(B) A screw gauge provided on the microscope
(C) A vernier scale provided on the microscope
(D) A standard laboratory scale

Answer 1

First let us see what a travelling microscope is: A travelling microscope is an instrument for estimating length with a resolution regularly for $0.1\,mm$. The precision is with the end goal that better-quality instruments have estimating scales produced using Invar to evade mis readings because of thermal impacts. The instrument includes a microscope mounted on two rails fixed to, or part of an unbending bed. The position of the microscope can be changed coarsely by sliding along the rails, or finely by turning a screw.

Complete step by step answer:
Travelling microscope is a compound microscope that is fitted on the vertical scale. It conveys a vernier scale along the fundamental scale and can be moved upward and vice versa.
At the point when a glass slab is put on a level surface, and its base surface is seen from the top, because of refraction, it gives off an impression of being raised. The obvious thickness of the slab is resolved from the separation between the apparent and the head of the glass section. The refractive index concerning the medium and air is given as:
$n = \dfrac{{{\text{real}}\,{\text{thickness}}\,{\text{of}}\,{\text{the}}\,{\text{slab}}}} {{{\text{apparent}}\,{\text{thickness}}\,{\text{of}}\,{\text{the}}\,{\text{slab}}}}$
Apparent shift is characterized as the distinction between the object's distance from the refracting surface and the image distance from the refracting surface. From the above discussion it is clear that in this experiment distances are measured by a vernier scale provided on the microscope.

Hence, option C is correct.

Note: In this experiment while finding the refractive index we should always remove the parallax. Also the microscope should be moved upwards. We should be careful while calibrating the scale also.