Reflection of Light:

When a beam of light travelling in a straight line homogeneous medium falls on the boundry of another medium, then a part of it bounces back from there, this bouncing back of the light is called the reflection of light.



Dependence of reflection of light
The amount of light reflected from the surface of another medium depends on

• Nature of the medium
• Smoothness of the medium.

Spherical Mirrors
A spherical mirror is portion o the reflecting surface of a hollow sphere.
Types

• Concave Mirror
• Convex Mirror

1. Concave Mirror: If the Inner surface of the spherical mirror is reflecting, then it is called a concave mirror.
2. Convex Mirror: If the outer surface of a spherical mirror is reflecting, then it is called the convex mirror.

SOME IMPORTANT DEFINATIONS

1. Centre of curvature: The centre of the hollow sphere of which mirror is a part, is called its centre of curvature.
2. Radius of Curvature:The radius of the hollow sphere of which mirror is a part, is called Radius of curvature.
3. Aperture: The front section of a spherical mirror is circular one and its diameter is called aperture.
4. Pole:The central point of a mirror is called its pole.
5. Principal Axis:The line joining the pole of the mirror and centre of curvature is called principle axis of the mirror.
6. Principle Focus:Rays of light parrallel to principal axis after reflection from a concave mirror converges to a point is called principal focus of the mirror.
7. Real and Virtual Focus:The reays of light parrallel to principal axis is realy pass through the principal focus then it is known as real focus.If the rays of light parallel to principal axis do not really pass through the principal focus , but seems through it then this is known as virtual focus.
8. Focal Length :The distance between principal focus and pole of the mirror s called its focal length.
   • Focal Length of concave mirror is positive
   • Focal length of convex mirror is negative.

USES OF SPHERICAL MIRRORS

CONCAVE MIRRORS

1. Concave Mirrors are used as shaving mirrors.
2. Concave mirrors are used as magnifiers
3. Concave mirrors are used to throw light on the slides of microscopeto view it more clearly.
4. These mirrors are used in search light and head lights
5. These mirrors are also used by doctors in their instruments for the examination of eye,nose ears and throat.
6. Some developed countries use giant mirrors in their huge telescopes.

CONCAVE MIRRORS

1. Convex Mirrors are used in motorcycles and automobiles to see the rear view.
2. Convex mirros are used in huge shopping centres for security purposes
3. Convex mirrors are used on the blind turns anddangerous turns.

REFRACTION OF LIGHT

The bending of light when it enters from one medium to another is called refraction of light.

LAWS OF REFRACTION
There are two laws of refraction of light.

• The incident ray, the refracted ray and the normal at the point of incidence all are in the same ratio.
• The ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant for a given pair of media.

CONDITION FOR REFRACTION

1. When a ray pf light passes from rare to denser medium, it bendds forward the normal.
2. When a ray of light passes from denser to rare medium, it bends away from the normal.

APPLCATIONS
Refraction of light may have given us false visual impression , but it does have many useful applications .Lenses are used in magnifying glasses,spactacles,microscopes, telescopes and overhead light rays passing through them produce the required images.

APPARENT AND REAL DEPTH
When we view an object at the bottom of a swimming pool, the object appears closer to the surface. This aparent depth is caused by refraction of light. It occurs due to fact the rays from an object under water do not travel straight to the eye but are refracted away from the normal as they leave the water surface. When these rays are produced backward, they meet and their images is formed so that the observer sees the object as that it were at the point of formation of tages.

APPARENT DEPTH
The distance of image from the surface of the water is called apparent depth.

REAL DEPTH
The distance of object from the surface of water is called real depth.

TOTAL INTERNAL REFLECTION

When a ray of light from denser medium enters a rare medium in such a way that the angle of incidence is greater than the critical , then they reflects totally inside and does not emerges out from the denser medium.This phenomenon is called Total internal reflection
When the value of angle s of incidence becomes greater than the criticale angles the rays does not pass into the second medium i.e the ray of light no longer suffer refraction but totally reflected back in the danser medium obeying laws of reflection.

Conditions for total internal reflection

1. The ray of light should travel from a denser to a rare medium.
2. The angle of incidence should be greater than the critical angle.

Dispersion of light
The phenom of splitting of white light into its colours is called dispersion of light.

The refraction of light depends on their wavelength.Since the sunlight consists of different colours the waves of different wavelength obtained. Therefore when light passes through a prism then the wave of different wavelength deviate on different paths due to dispersion of light.
The band of colours which is seen on the the screen due to passage of sunlight through the prism is known as solar spectrum..

RAINBOWS
An arc of spectral colours, which appears in the sky after the rainfall is called rainbow.

How rainbow is formed?
Rainbow is solar spectrum produced due to dispersion of light. After the rainfall, innumerable droplet of water remain suspended high up in the air. When sunrays fall on these droplets each droplet behaves likes a prism and light rays enterig, the droplets suffers refraction and total internal reflection. Since these rays are white light, they split into seven colurs.

CONDITIOn
Rainbow is the most beutifu and colourful natural ph whcih can be seen on the sky.
The viewers can see the rainbow when the sun is at the back of the observer.
When sunrays fall obliquely.
Rainbow can be seen in the morning or in evening.

TYPES OF RAINBOW

1.Primary Rainbow
Such rainbow has brightest colours and is easily visible .
Characteristis

• In primary Rainbow, the rays fro the sun suffer only one total internal reflection in rain droplet.
• It has brightest colours and is easily visible
• It has red colour on its outer edge and voilet colours on its inner edge.
• In primary rainbow the colour are in the order of red ,orange ,yellow ,green, blue, indigo, and voilet.

2.Secondary Rainbow
Such Rainbow which is fainter than primary and is seldom visible called secondary rainbow.

Characteristis

• In Secondary Rainbow, the rays fro the sun suffer double total internal reflection in rain droplet.
• It has faintest colours and is seldomvisible
• It has voilet colour on its outer edge and red colours on its inner edge.
• In primary rainbow the colour are in the order of voilet , indigo,blue, green,yellow, orange, red

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