Max Planck was attempting to derive mathematical equations to
describe the spectrum of the radiation given out by a hot body. 



He found that his equations could not be made to agree with
experimental data as long as he considered electromagnetic
radiation to be continuous. 

In order to solve this problem, he made the following
suggestions 



1. 
Electromagnetic radiation is
quantized (radiated in "packets" of energy called
quanta or photons) 
2. 
The amount of energy carried by
each quantum is directly proportional to the frequency
of the radiation. 




Notice that these two statements could be considered to be
confusing. 

Statement 1 suggests that EM radiation consists of
particlelike entities and yet statement 2 refers to the frequency
of those same radiations! 



Don't worry if this sounds strange... it is still not fully
understood what EM radiations like light really are. 

However, the one thing we can say for sure is that these
radiations exhibit both particlelike and wavelike
behaviours. 



The energy possessed by a quantum is given by 



or, in terms of wavelength 



where h is a constant, now called Planck's constant, which has a
value of 6.63×10^{34}Js 



Notice that this is a very, very small figure which
explains why we don't normally observe the discontinuous nature of
light (and other EM radiations) in everyday life. 

The size of the individual packets of energy is very small, thus
giving the illusion of a continuous stream of... something... 



From Planck's simple sounding suggestions has developed what has
been called the most successful physical theory ever...
quantum mechanics. 
