Ray Optics – Notes – 1


When a ray of light falls on a surface and returned into the same media, then this phenomenon, is called reflection of light.

Laws of Reflection

The reflection at a plane surface always takes place in accordance with the following two laws :
(i) The incident ray, the reflected ray and normal to surface at the point of incidence all lie in the same plane.
(ii) The angle of incidence, i is equal to the angle of reflection r, i. e., ∠i = ∠r.


Figure-1 : Reflection

i = Angle of incidence
r = Angle of reflection

#Note : 
1. After reflection velocity, wavelength and frequency of light remains same but intensity decreases.
2. If light ray incident normally on a surface, after reflection it retraces the path.

Total Internal Reflection :

When Angle of incidence exceeds the critical angle than light ray comes back in to the same medium after reflection from interface. This phenomenon is called Total internal reflection.

When a ray of light goes from denser to rarer medium it bends away from the normal and as the angle of incidence in denser medium increases, the angle of refraction in rarer medium also  increases and at a certain angle, angle of refraction becomes 900, this angle of incidence is called critical angle.

2016-07-06_10-54-32Figure-2 : Total internal reflection

i = Angle of incidence
r = Angle of reflection
C = critical angle

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