Max Planck in 1900 stated that radiation is neither absorbed nor emitted continually. It is done so in the form of quanta or photon.
The following statement is now the basis of quantum physics which in turn of modern physics. So to understand what a “quanta” is, let us take an example.
Suppose you want only one biscuit. So when you go to a store will you get as one biscuit? No, you will get as a packet containing 10 biscuits. So, even if you wanted to have only one biscuit, you have to buy the entire packet for one biscuit. Such is the quantum theory.
Even though you might require only say 5 joules of energy, what is available to you is a packet of energy or “quantum”. The success of this theory comes as it is the first theory which almost successfully explains light and some of its properties like photoelectric effect.
The equation for energy of ‘n’ number of quanta is given as:-
E = hv
Where ‘h’ is Planck’s constant with value as 6.6256 x 10-34 Joule-second and ‘v’ is frequency of light.
But this was not until 1905 was that the theory was believed by Einstein and used this theory to explain photoelectric effect and was awarded Nobel Prize for it in 1921.