There are two different ideas about the nature of light or electro magnetic radiations.

1. Particles:

As per Quantum theory the light arrives as a packets of energy at a 'target'. They are called as photons. They produce a particle picture of light. This particle is responsible for the phenomenon called the photoelectric effect e.g. Photgraphy, vision etc.

2. Waves:

There are cases where the functions depicted by light can only be best understood by depcting the light as a wave. In these cases light can be expressed as a wave or expressed in mathematical fuctions called wave functions. For eg: in the case of rainbow. In the early 1920's Louis De Broglie suggested the wave properties could also be associated with particles. He also showed a general wave mechanic method for handling atomic and molecular systems. Thus the wavelength, l of the wave can be calculated by using. The electromagnetic wave equation, e = hn -------- (1)

where h = Planck�s constant.

n = frequency of photon.

e = energy of photon Einstein energy-mass relation.

. This reference shows how a wave look like.

Einstein energy-mass relation

e = mc2 -------- (2)

where m = mass of photon

c = speed of light and

n = c / l -------- (3)

where l = wavelength of photon

n (greek alphabet Nu) = frequency of photon

c = speed of light. Thus we get hn = mc2 -------- (4)

h (c / l) = mc2

h / l = mc

l = h / (mc) -------- (5)

Thus, this equation gives us the wavelength of an electromagnetic radiation ( i.e. in this case a photon) in terms of h, Planck constant; m. mass of photon; and c, the speed of light.

Thus, the following relation can be used to calculate wavelength of beams of particles with velocity u (greek alphabet Upsilon), mass m and h as a Planck�s Constant.

l = h / (mu) -------- (6)

This is known as de Broglie Relation/Equation.

Quantum Theory Contd...

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