What is light?

                                   

Light is an electromagnetic wave.  It consists of particles of energy called photons. Each photon consists of a fixed amount of energy called quantum. Each quantum consists of a wave of wavelength, λ and frequency, v. The energy of a photon, E is equal to- 

                                                     E = hv = hc/λ                (c = vλ )

                                     where,     h = Planck's constant = 6.625 X 10^-34

                                                     ^{v = frequency of the wave}

                                                     ^{c = speed of light}

                                                     λ = wavelength

^{Thus, a light wave can have energies in the multiples of hv i.e. hv, 2 hv, 3 hv etc.}