The students The students Understand the phenomena of total internal Understand the phenomena of total internal reflectionreflectionAppreciate the applications of total internal Appreciate the applications of total internal reflection in various fields reflection in various fields Develop logical reasoning abilityDevelop logical reasoning abilityAre Exposed to the use of Total Internal Are Exposed to the use of Total Internal Reflection in modern communication systemsReflection in modern communication systems
The students already knowThe students already know
• The phenomenon of Reflection and The phenomenon of Reflection and RefractionRefraction
• Laws of Reflection and RefractionLaws of Reflection and Refraction
What is Refraction?What is Refraction?
• Refraction is the bending of light at the surface of separation between two transparent media when light passes from one medium to another
• Light bends towards the normal when it travels from a rarer to denser medium
• Light bends away from the normal when it travels from a denser to rarer medium
Consider a ray of light travelling from a denser to rarer medium
The ray of light bends away from the normal in the rarer medium
Denser medium
Rarer medium
• The refracted ray bends more away from the normal and nears the surface of separation.
Now let’s increase the angle of incidence
Denser medium
Rarer medium
Now for a particular value of angle of incidence the refracted ray grazes the
surface of separationThis angle of incidence inside the denser medium, for which This angle of incidence inside the denser medium, for which
the refracted ray just grazes the surface of separation is the refracted ray just grazes the surface of separation is called the critical angle for the pair of media.called the critical angle for the pair of media.
What happens If the angle of incidence inside the denser medium
is greater than the critical angle?Then the ray is not refracted, But it is totally reflected internally obeying the laws of reflection. This phenomenon is called TOTAL INTERNAL REFLECTION
CONDITIONS FOR TOTAL INTERNAL REFLECTION
1.1. The light must travel from a denser to The light must travel from a denser to a rarer mediuma rarer medium
2.2. The angle of incidence must be The angle of incidence must be greater than the critical angle for the greater than the critical angle for the pair of media.pair of media.
APPLICATIONS OF TOTAL INTERNAL REFLECTION
• TOTAL REFLECTING PRISMS
• SPARKLING OF DIAMOND
• SHINING OF AIR BUBBLE IN WATER
• MIRAGE
• OPTICAL FIBRES
TOTAL REFLECTING PRISMS
• THEY ARE ISOCELES RIGHT ANGLED PRISMS
USES OF TOTAL REFLECTING PRISMS
• TO ROTATE A RAY OF LIGHT THROUGH 90
TO ROTATE A RAY OF LIGHT THROUGH 180
TO ERECT AN INVERTED IMAGE OR VICE VERSA
SPARKLING OF DIAMOND
SHINING OF AIR BUBBLES IN WATER
MIRAGEMIRAGE
OPTICAL FIBRES
ACKNOWLEDGEMENTS
NCERT Text Book for Class XII and http://www.ncert.nic.in for content