5.3 Understanding total internal reflection of light

~Total internal reflection is the total reflection of a beam of light at the boundary of two mediums,when the angle of incidence in the optically denser medium exceeds a specific critical angle.
~The Critical angle is the angle of incidence in the optically denser medium for which the angle of refraction,
   r = 90degree
~conditions required for the occurrence of total internal reflection :
   (a) light ray must travel from an optically denser medium to a less dense medium.
   (b) angle of incidence must be greater than the critical angle,that is ,i >c


Relationship between Critical Angle,c and Refraction Index,n
~The refractive index of glass,
n=sin i(in air)/sin r(in glass)
  =sin 90 degree/sin c
  =1/sin c


Effect of a prism on light rays
~The rays of light are deflected by 90 degree.

~The two rays of light are inverted.

~The two rays of light are deflected bu 180 degree.

Natural Phenomena and the Uses of Total Internal Reflection

(a)A rainbow formed because of refraction,dispersion and total internal refraction of light which passes though     water droplets in the air,

(b)Light is refracted and dispersed into its various colour components when it enters the raindrops.

(c)It then undergoes total internal reflection at the back of the raindrops and then refracted again as it leaves.

(a)A fish or a diver is able to see an object above the water surface because the rays of light from the object are refracted to the eyes of the fish or diver.

(b)Due to total internal reflection,part of the water surface acts  as a perfect mirror,which allow the fish and diver to see objects in the water and the objects around obstacles.

Applications of Total Internal Reflection

1.The critical angle of glass is around 42 degree.

2.A prism is made of a high-density optical medium such as glass.

3.When light from the air strikes a prism at right angle,no refraction occurs.If after through the prism,it hits the  opposite surface,internal total reflection occurs.Because the angle of incidence which is 45 degree is greater than the critical angle of glass which is only 42 degree.

~A prism is a better reflector compared to a mirror because of the following reasons.

(a)Ordinary mirrors give multiple images due to multiple reflections in the glass at the front of the mirror.

(b)The silvering on the mirror is easily damaged.

(c)A mirror reflects less light than a totally-reflection prism.