According to Eienstein’s quantum theory light propagates in the from of bundles (packets or quanta) of energy, each bundle is called a photon and possessing energy.
(1) Energy of photon: Energy of photon is given by
E = hv hc/λ ;
In electron volt E(eV) = hc/eλ = 12375/λ(Å)
(2) Mass of photon
E = mc2 = hv m = E/c2 = hv/c2 = h/cλ
(3) Momentum of the photon
Momentum p = m×c = E/c = hv/c = h/λ
(4) Number of emitted photons: The number of photons emitted per second from a source of monochromatic radiation of wavelength λ and power P is given as (n) = P/E = P/hv = Pλ/hc;
E = energy of each photon
(5) Intensity of light (I): Energy crossing per unit area normally per second is called intensity or energy flux
i.e. I = E/At = P/A
I = P/4πr2 ⇒ I ∝ 1/r2
I ∝ P/2πrl ⇒ I ∝ 1/ r.