Speed of Light and Reflective Index - Physics
13-02-2020    115 times

### Speed of light

The speed of light in vacuum and air is 3 x 108 ms-1. It is the maximum speed of light. The speed of light in air or vacuum is denoted by a symbol c. In any other transparent media (water, oil, glass), the speed of light is slower than c. The reflective index of a medium can define with respect to vacuum or air is known as absolute reflective index.  It is denoted by μ or n.

As we know, v is always less than c, therefore μ is always greater than 1. The reflective index of alcohol is 1.37. That means light travels in air or vacuum 1.37 times faster than in alcohol.

Reflective index of some common substance

 Substance μ or n Substance μ or n Vacuum or air 1.00 Ice 1.03 Water 1.33 Methylated spirit or Ether 1.36 Alcohol 1.37 Kerosene 1.41 Sulphuric Acid 1.43 Paraffin Oil 1.44 Glycerine or turpentine oil 1.47 Glass 1.5 Diamond 2.41 Ruby 1.67 Flint Glass 165 Rock salt 1.56 Crown glass 1.53 Quartz 1.54

### Reflective index of a medium in respective of another

In there are two different medium is present, in which the light is travel. Then we can calculate the reflective index of a medium in respective of another. Let there are two medium m1 and m2.

Example -

The reflective index of glass is 3/2 and reflective index of water 4/3.

Given,          aµg = 3/2, aµw = 4/3

Therefore, wµg = (Reflective index of glass) / (Reflective index of water) = (3/2) / (4/3) = 9 / 8 = 1.125.