# Introduction to Speed of Light in Air

The speed of light is denoted by c is a physical constant used in physics. This is the speed at which light and all other electromagnetic radiations travel in vacuum irrespective of the motion of the source or observer.

The value of speed of light is exactly 299,792,458 meters per second.

In terms of theory of relativity, it comes under space and time in equation of mass : E = mc2.

Speed of light is the speed of all mass less particles in vacuum. speed at which light propagate through transparent materials is less than c.

The ratio at which c and v travels in a material is called refractive index (n) of materials: [ n="c/v" ]

## Notation of Speed of Light

The speed of light is dimensional physical constants, so numerical value depends on the SI units.

So, meter is used to define the distance light travels in vacuum in certain time intervals.

Speed of light is 3 x 108 meter/seconds.

## Role in Physics

The speed at which light propagates is independent of the light source and the observer which was postulated by Albert Einstein in 1905, used in many experimental purposes.

In physics generally the speed of light is isotropic means c has same value regardless of propagation.

## Propagation of Light

Light is described as a type of electromagnetic wave which relates speed c with which such waves propagate through vacuum is related to electric and magnetic constant. So,

c = 1/√e0µ0

In quantum physics the electromagnetic field is described by theory of quantum electrodynamics, where light is described as fundamental excitations of electric fields called Photons.

Photons are mass less particles, thus they travel at speed of light in vacuum.

Speed of light generally varies with frequency because of special relativity as predicted by theories of quantum gravity.

In a medium light usually does not propagate with speed equal to c, different types of light sources travels at different speeds.

The speed at which though and crest of plane wave propagate is called a phase velocity. This helps in determining how a wave propagate through a material or between two materials that is represented in terms of refractive index.

In case of transparent materials, refractive index is generally greater than 1 means that phase velocity is less than c.

## Important Points on Speed of Light

Speed of light has implications on various sciences and technologies

Speed of light has some relevance to communication.

Consequence of finite speed of light results in non instantaneous communication between Earth and spacecrafts.

In case of supercomputers, speed of light implicates the rate of data sent between processors.

Radar systems measure the distance of target using the speed of light.

A GPS receiver measures its distance to GPS satellites based on radio signals which in turn uses speed of light to transmit signals to receiver based on distance.

To measure speed of light, various techniques were used such as astronomical phenomena, experimental setups etc on Earth.

Speed of light is measure in meters, which is defined as length of the part travelled by light in vacuum during a time interval of 1 / 299,792,458Th of a second.

## Snapshots on Speed of Light

My forthcoming post is on Refraction Of Light, Velocity and Speed will give you more understanding about Physics.