THEORIES OF LIGHT

In this topic we will learn about light. How lights originates and What are the theories of light. We will also discuss the modern theories of light. We will start with Corpuscular Model of Light. Which was given by Issac Newton. According to corpuscular model of light “ A luminous body (luminous means bright in colour) emits stream of particles in all direction .“ the emitted particles were assume that very tiny in size, due this overlapping between two particles or collision between two particles are rearly occur. Using corpuscular model we can explain law of reflection of light and law of refraction of light. In order to explain law of reflection  we have to consider the elastic reflection of particles by plane surface. And in order to explain law of refraction we must consider the motion of particle confined in x-y plane. The trajectory of particle is determined by conversion of x-component of momentum (psinQ) where Q is angle that the direction of propagation make with y-axies ).
Perhaps there are two most important experimental facts which lead to belief the corpuscular model of light. These experimental facts are-

•  The rectilinear propagation of particles of lights which results in formation of sharp shadow.

• That light could propagates through vacuum.

However , when experiment were conducted then its observe that the shadow formed of object is not perfectly  dark. Its means some lights enter in geometrical shadow. This is due to the scattering of light. For example-you can study in shadow of tree. The lights is coming in shadow is due to scattering of lights through molecules of air. This phenomenon of scattering of lights by air molecules is responsible for blue colour of sky. If we are talking about the moon, at which have almost no atmosphere. Then a shadow formed on moon surface is perfectly dark in colour. Because there is no scattering of lights takes place.

Now we will learn about The Wave Model of Lights. First of all you have to understand  that what is wave? In shorts we says that “A wave is propagation of disturbance.” For example- when we through a stone in clam pool of water, then we observe that a circular pattern spread out from the point of impact. The stone create disturbance, that propagates outward. This is example of transvers wave. we can also say that, wave is nothing but transfer of energy. In above case energy is in form of kinetic energy of water molecules. There  is lots of types of waves and all waves are characterized by certain properties such as wavelength and frequency.