6. Plank's quantum theory and Radiant energy

Radiant energy-

       It is a most powerful natural source of energy.It travel in the form of wave .It can be visible or non visible some time ...It  is used in the field of Radiometry, solar energy, heating , lighting ..etc. and also in the field of telecommunication.

Concept of radiant energy -
 -According to j.c. Maxwell (1864), alternating currents of high frequency is capable of radiating energy in the form of waves.
-These waves travel in space with the same speed as light,these waves are called as electromagnetic waves or electromagnetic radiations.

 -This  electromagnetic radiation is a form of energy which propagate through the space in the form of waves which are associated with electric and magnetic field.
- Velocity of radiation  
                              C = λv,
            Where v is frequency, and λ is wave length of the radiation.

All type of  electromagnetic radiation travel with the same velocity but they differ in their frequency and wavelength.


Plank's Quantum Theory of Radiation- Theory to explain spectral distribution of radiant energy

According to Plank's Quantum theory..

1. Radiant energy is not emitted or absorb continuously but discontinuously in the form

of small bundles of energy  called as Quanta.

2. The  quantum of light is called photon (i.e.  mass less bundle of energy )

3.Each quantum is associated with a definite amount of energy E  which is proportional
to the frequency of radiation  
                            
                               E = hv

where h= plank's constant and (h=6.62688x10⁻²⁷ erg sec or 6.626x10⁻ᶟ⁴J s.)

A body can absorb or emit energy in whole number multiples of quantum, i.e.  E=nhv
   where n = 1, 2, 3, ....

This means body can absorb or emit  energy equal to 1 hv, 2 hv, 3 hv...etc. Energy in fraction can't  be absorbed or lost.

     This is called quantisation of energy.