# Importance of Velocity of Light

The value of velocity of light in vacuum is of great importance in science. The following are some of the important fields where the value of velocity of light is used.

(1) Frequency – wavelength relation: From the relation c = vλ, the frequency of electromagnetic radiations can be calculated if the wavelength is known and vice versa.

(2) Relativistic mass variation with velocity: Theory of relativity has shown that the mass m of a moving particle varies with its velocity v, according to the relation m = m0/√{1 –(v2/c2)}.

Here m0 is the rest mass of the particle.

(3) Mass – Energy relation: E = mc2 represents conversion of mass into energy and energy into mass. The energy released in nuclear fission and fusion is calculated using this relation.

(4) Measurement of large distance in Astronomy: Light year is a unit of distance used in astronomy. A light year is the distance travelled by light in one year. It is equal to 9.46 x 1015 metre.

(5) Refractive index: The refractive index μ of a medium is given by

μ = [velocity of light in vacuum / velocity of light in medium] = c/v