Explain the Planck's quantum theory. 

 Planck's quantum theory

1)Substances absorb (or) emit light discontinuously in the form of small packets (or) bundles.
2) The smallest packet of Energy is called quanta.
3) The emitted radiation is propagated in the form of waves.
4) The energy of a quantum is directly proportional to the frequency of radiation.
$\mathrm{E\alpha \vartheta }$
The energy of a quantum is
$\mathrm{E}=\mathrm{h\vartheta }=\mathrm{h}\cdot \frac{\mathrm{c}}{\mathrm{\lambda }} \left(\because \mathrm{\vartheta }=\frac{\mathrm{c}}{\mathrm{\lambda }}\right)$
$=\mathrm{hc}\overline{\mathrm{\vartheta }} \left(\because \overline{\mathrm{\vartheta }}=\frac{1}{\mathrm{\lambda }}\right)$
Where E = Energy in ergs.
h = planck’s constant
$=6.625\times {10}^{-27}\text{ erg.sec }$
$=6.625\times {10}^{-34}\text{ Joule.sec }$
5) A body can absorb (or) emit energy in whole number of quanta $\mathrm{E}=\mathrm{nh\vartheta }$
n = 1,2,3,4..........etc (or)
Plack’s quantum theory :
1) Absorption (or) emission of light by the substance is always in discontinuous manner in the form of small packets or bundles.
2) The Smallest packet of energy is called quanta.
3) The radiation is travel in the form of waves.
4) Energy is directly proportional to frequency of radiation.
$\mathrm{E\alpha \vartheta }\Rightarrow \mathrm{E}=\mathrm{h\vartheta }$
Where E = Energy of light; h = placks constant
$=6.625\times {10}^{-27}\text{ erg.sec }$
$=6.625\times {10}^{-34}\text{ Joul.sec }$
$\mathrm{\vartheta }$ = Frequency of light
5) A body can absorb (or) emite energy in whole number of quantum.
i.e E = n h$\mathrm{\vartheta }$ ; n = 1, 2, 3, 4 …….