LIGHT REFRACTION TOTAL INTERNAL REFLECTION OPTICAL FIBRES BY : A. Ananda Military School Bangalore

 B ending of light when it travels from one optical medium to another is called refraction.  T he ray of light bends towards the normal when it travels from rarer to denser medium. he ray of light bends away from the normal when travels from denser to rarer medium.

 The ray of light is refracted because the speed of light is different in different media.

ILLUSTRATIONS:  A coin placed under water appears raised.  A stick immersed in water partially, appears bent.

Laws of refraction:  The incident ray, the reflected ray and the normal drawn at the point of incidence all lie in the same plane  For a given pair of media and given color the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant # This is called Snell’s law # The ratio is called the refractive index of the medium represented by µ = sin i/sin r

 Refractive index is also given by: =  Velocity of light in air or vacuum Velocity of light in medium

© Refracted ray bends away from the normal when it travels from denser to rarer medium. © As the angle of incidence is increased, angle of refraction also increases. © For a particular angle of incidence in the denser medium called critical angle, the angle of refraction in the rarer medium is 90 o

C 90 o water air © For any angle of incidence greater than critical angle, the ray of light turns back to the same medium. © This is called total internal reflection. Object

 For critical angle; since light is traveling from denser medium to rarer medium:- CONDITIONS FOR TOTAL INTERNAL REFLECTION:  The ray of light should travel from denser to rarer medium.  Angle of incidence should be greater than critical angle for a given pair of media. 1 = sin i = sin c = sin C  sin r sin 90 o 1 OR  = 1/sin C

 Ex : Critical angle with air for different media- Water = 48 o Glass = 42 o diamond = 24 o ILLUSTRATIONS:  Mirage – an optical illusion that appears in deserts during summer

 Looming : The image of ship appears hanging in air due to mist and fog for a person on the shore.  Sparkling of diamond.

APPLICATIONS:  Total reflecting prisms: i)To turn a ray through 90 o Used in periscope ii) To turn a ray through 180 o 90 o

iii)Erecting prism: Used in prism binoculars 90 o

 OPTICAL FIBRES: USES:  In medicine – Endoscopes  Optical sensors – used computers and detectors  Telecommunication.  Laser probes, etc.,

Sources : © Science encyclopedia – CD ROM D K Multimedia 1. Mirage. 2. Looming. 3. Optical fiber © NCERT Text. Presented by: A Ananda Military School Bangalore