Speed of light
- The rate of Light is 3 x 106 m/s. The and the light’s in common glass is 2*10^8 m/s.
- That is precisely 3,00000 km per second in a vacuum.
Speed of Light in Different Media
- Light travels maximum in a vacuum and with different speeds in a different mediums.
| Substance | Speed of light (ms-1) | Refractive Index (𝝁) |
| Water | 2.25 x 108 | 1.33 |
| Glass | 2 x 108 | 1.5 |
| Diamond | 1.25 x 108 | 2.41 |
| Air | 3 x 108 | 1 |
Note: The refractive index of a medium is also defined in terms of the speed of light in different media.
𝝁 = speed of light in vacuum or air (c ) / speed of light in a medium (v)
In general 𝝁 (Refractive Index) = speed of light in medium 1 / speed of light in medium 2
The speed of light in a vacuum is denoted as ‘c’. It is a universal constant.
Reason for the speed of light different in different mediums
The speed of light is decreased when travels through transparent media such as air, water, glass etc. The ratio by which the speed of light is decreased is called the refractive index of the medium and is always greater than one.
Which medium is light the fastest?
The light travels at maximum velocity in a vacuum. The vacuum has less refractive index than Air. Air has a refractive index of 1.003.