Light : Reflection and Refraction

Light : is a form of energy which enables us to see objects from which it comes (or from which it reflects.)

Luminous objects :

Those objects which gives out their own light are called luminous objects. examples are sun , candle, Lamp etc

Non-Luminous objects : 

Those objects which are unable to gives out their own light (which only scatter or reflects only ) are called luminous objects. examples are moon , chair , table etc.


[Note : Light travels only in straight line.]


Nature of light

Light has a dual nature (double nature) actually light exhibits the properties of both waves and particles (depending upon the situation) and this modern theory of light is called “Quantum Theory of Light” . 

Lets talk about wave theory of light : According to wave theory of light , light consist of electromagnetic waves which do not requires any medium (solid , liquid or gas) for its propagation. The light waves have very small wavelengths approx ​\( 4\times{10^{-7}} \)​ m to ​\( 8\times {10^{-7}} \)​ m . And the speed of light waves are around ​\( 3\times{10^{8}} \)​ meter per second . 

Particle nature of light : According to particle theory of light , light is composed of particles which travels in a straight line at very high speed. The elementary particles of light are “photons” .

The reason behind the acceptance of both the theory is that some of the property of light can only be explained is light is considered to be a wave example diffraction (bending of light around corners) , interference and polarization . And where as some property of light only be explained is light is considered to be a particle example formation of shadow , reflection and refraction .


What happens when light falls on objects

When light rays fall on the surface of objects some of it get (i) Reflected , some are (ii) Transmitted ,  and some are (iii) Absorbed.

Reflection : 

The process of sending back the light rays which falls on the surface of an object is called reflection of light.

Some object completely reflect light and some reflect very few ,mostly shiny and smooth surface reflects more light than the rough and dull surface. 


Refraction : 

When a object transmits (passes) light through itself , then the object is said to be transparent . example : ordinary glass (most of light is transmitted). Now come to the point , When light rays is transmitted (passes) through a transparent surface it bends from its original path and this bending is called refraction of light.


Absorption : 

From the name itself it is clear that some light also get absorbed when light rays falls on the surface of object.


[ Note : Silver metal is one of the best reflectors of light.]

How a ordinary plane mirror is formed ?

Ordinary mirror is made by polishing a thin layer of silver metal on one side of a plane glass sheet and then the silver layer is protected by coating of red paint (this is just to prevent scratch on silver mirror).


How we represent plane mirror in diagrams ?

We simply show plane mirror by straight line(side of reflection) having a number of short , oblique line on one side (coated side).


How we represent light rays in diagrams ?

By just a straight ray,arrow in the direction of light .

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