light is an energy which travel as an electromagnetic wave . I know the light through our eyes . The theory of electromagnetic of light explains the some quality of light ; reflection of light , refraction of light , Total internal reflection of light , optical fibres , dispersion of light, interference of light etc.
There are many types of ray . light is also a ray . The ray which is come from source light is called incident ray. And the ray which is comeback from an opaque substance is called reflected ray. speed of ray is different in different medium . speed of light ray is about 300000 m/sec.
some important facts of light which you remember for exams.
Light travels in a straight path of medium . electromagnetic wave is a transversal wave . so, light is a transversal wave . its wavelength is between 3900A to 7800A.
you must know about Mr. Jadd-Johnson which explains the electromagnetic wave is a transversal wave . electromagnetic wave is double nature wave and particle .in this chapter we study about the properties of light . light follow some rules of wave and some lows of electromagnetic wave . Both theory is essential for light .
refraction of light
in general light travel in straight path of medium but when light pass from one medium to another (rare medium to denser medium ) the path of light is differ from its own path . This phenomena is called refraction of light . we understand this phenomena through some example.
you will take a glass of water and sink a straight stick such as some parts of stick is above the water. then you can see the stick seems like curve but it is only straight stick.why its is seems like curve ?
Because it is the phenomena of refraction of light .
when you put a coin in a glass of water , you seem like the coin is above the bottom of the glass , it is also the phenomena of refraction of light.
if you see sky at night ,you can see the stars twinkle in the sky but it is not in originally. it is also the example of refraction of light .
if you see the sun in the morning and the evening ,you can see the sun after sometime sunrise and sunset. it is also the phenomena of refraction of light. I hope you understand the refraction of light.
There are two laws of refraction of light:-
1.incident ray, refraction ray and normal of the refraction is always lies in same plane.
2. for two medium , the sine of angle incident and sine of angle of refraction is always constant.
now we learn the reflection of light.
reflection of light
some things allow to pass the light but some are not . which things do not allow to pass the light through own is called opaque .
when light pass through an opaque substance which not allow to pass the light, so light come back to the same medium .This phenomena is called reflection of light. some example of reflection given below.
when you take a mirror in the direction of light come from the light is come back the opposite direction. This is reflection of light .
There are two rules of reflection :
1. incident ray , reflected ray and normal of the incident is always lies in same point.
2. Angle of reflection is equal to the angle of incident.
when the ray incident bump into an opaque substance an angle be makes with normal to incident ray , is called angle of incident . And the angle which is makes with normal to reflected ray , is called angle of reflection .
behaviour of light there are many types of substance such as :
Luminous bodies :-
The body which has its own light and heat is called luminous bodies. example; sun , star , electric bulb etc.
Nonluminous bodies :-
The body which has no own light and heat is called Non-luminous bodies . such substance is lighten with other luminous objects. example moon, table, chair etc.
Transparent bodies :-
The object which allow to pass the light through its own body is called transparent bodies. example -glass, water
Translucent bodies:-
The body which allow to pass some amount of light from their body is called translucent bodies. example -oily paper,
Opaque bodies :-
The body which do not allow to pass the light through their body is called Opaque bodies . example- wood, stone, wall.
now we study the speed of the light . speed of the light depend on medium of the substance which has made from.
speed of the light is explain at 1st British physician Romar. He studies speed of light in several substance .
speed of light in vacuum :-30000000 m/sec
in air :- 30000000 m/sec
in glass :- 20000000 m/sec
in water :- 225000000 m/sec
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