In Class 10 Physics (Light: Reflection and Refraction), you learn that light bends (refracts) when it enters a new medium because its speed changes. The amount of bending is measured by the Refractive Index.
Formula: n = c / v.
Refractive index of Air: 1.0003 (~ 1).
Refractive index of Water: 1.33.
Refractive index of Diamond: 2.42 (Highest).
The Absolute Refractive Index (n) of a medium is the ratio of the speed of light in a vacuum (c) to the speed of light in that specific medium (v).
Formula: $n = \frac{c}{v}$
Note: Because it is a ratio of two speeds, the refractive index has no unit.
The absolute refractive index of air is 1.0003. For mathematical calculations, it is generally taken as 1.
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