TOTAL INTERNAL REFLECTION

 WHAT IS TIR ?

When a ray of passes from denser medium to rare medium , it is deviated away from normal .

If we increase the angle of incidence then the angle of incidence then the angle of refraction also 

increases . Then at a particular angle of incidence(C)the angle of refraction is 90 degree. This angle C

is known as critical angle.

If the angle of incidence is greater than critical angle then ray of light is totally reflected back in the same medium . This phenomenon is called as TIR. 

 CONDITIONS FOR TIR 

 

1. Ray must move from denser to rarer medium. 

2. Angle of incidence must be greater than critical angle.

APPLICATIONS OF TIR 

1. The brilliance of diamonds is due to TIR. 

2. Totally reflecting prisms. 

3. Mirage

4. Optical fibre

                    

                 

OPTICS PART 1 - RAY OPTICS

                              RAY OPTICS   

SPHERICAL MIRRORS

 It is the part of a hollow sphere whose one side is reflecting and other is opaque (silvered) .

There are two types of spherical mirrors :

1. Concave Mirror - It is a part of hollow sphere whose outer part is silvered and inner part is 

    reflecting . ( converging mirror )

2. Convex Mirror - It is a part of hollow sphere whose inner part is silvered and outer part is 

    reflecting . ( diverging mirror)

                                             

FOCAL PLANE

It is the plane passing through principal focus and perpendicular to principal axis.

RELATION BETWEEN FOCAL LENGTH AND RADIUS OF CURVATURE FOR CONVEX MIRROR ( F = R/2 )

        

angle ABE = angle DBE [law of reflection]                 -   1

angle ABE = angle BCF [ corresponding angle ]          -   2

angle DBE = angle CBF [ opposite angles ]                 -    3

from 1,2 and 3

angle BCF = angle CBF

therefore, BF = CF

As aperture is small so B is very near to P

therefore  PF = CF 

So F is the centre of PC

therefore PF = PC/2

or F = R/2 

KEY POINT

If mirror is immersed in any liquid there is no change in its focal length.

APPLICATIONS OF SPHERICAL MIRRORS

( A)  CONVEX MIRROR

      1. It is used as driver' s mirror because itt produces erect and small image, so field of view is 

          increased .

         

  2. It is used as a reflector in street lights.

        

                       

( B)  CONCAVE MIRROR

    1. It is used in shaving.

    2. It is used in solar cookers.

    3. It is used in dish antennas. 

    4. It is used in reflecting type telescope.

Reflecting Type Telescope

  

          

OPTICS

                   REFLECTION OF LIGHT

It is the bouncing back of the light in the same medium when the light falls on a surface.

LAWS OF REFLECTTION

1. Angle of incidence is always equal to the angle of reflection.

angle i = angle r

2. The incident ray , reflected ray and normal are coplanar.

where i = angle of incidence

           r = angle of reflection

SOME CHARACTERSTICS OF REFLECTION

1. If object moves with a velocity v ( say 10 m/s ), the image will move with a velocity 2v (20 m/s)

    in plane mirror.

2. If height of a person is 170 cm , then then to see full image, the length of plane mirror required is 

    170/2 = 85 cm.