High School Physics

# What is Refractive Index? – definition & formula | Refractive Index sample values

Last updated on November 26th, 2022 at 10:25 am

What is Refractive Index?
When a ray of light passes from the first medium to the second medium, the refractive index of the second medium with respect to the first medium is defined as the ratio of the sine of the angle of incidence (in the first medium) to the sine of the angle of refraction(in the second medium).
It is denoted as 1µ2. Here the letter µ is a Greek letter (pronounced as mew).

## Define Absolute Refractive Index (or Refractive Index RI)

The concept of the Absolute Refractive Index (also called Refractive index or RI) of a medium is brought into the picture to come up with a RI value for every relevant medium with respect to a common medium (vacuum or air is selected here).

Hence, the Absolute Refractive Index (also called Refractive index or RI) of a medium is defined as the ratio of the speed of light in a vacuum (or air) to the speed of light in that medium.
µ = speed of light in vacuum(or air) / speed of light in that medium = c/V

## The formula of Refractive Index or RI | Equation of refractive index

Formula 1:
1µ2 = RI of second medium with respect to first medium = (sin i) / (sin r)
where i = angle of incidence in the first medium
and r = angle of refraction in the second medium.

Formula 2:
1µ2 = RI of the second medium with respect to the first medium
= (speed of light in medium 1) / (speed of light in medium 2)

Formula 3 (Absolute Refractive Index – also called Refractive index or RI of a medium)
µ = speed of light in vacuum(or air) / speed of light in that medium = c/V

See also  Refractive Index (µ) of some common substances | Refractive Index Table

## Refractive Index (µ) of some common substances | RI sample values

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