Nov. 4, 2019



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/ = 12375/λ(Å)

(2) Mass of photon

E = mc2 = hv m = E/c2 = hv/c2 = h/ 

(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.