Reflection of Light

Reflections happen when light hits surface of a medium (incident ray), and bounces back (reflected rays). In other words, reflected waves are neither transmitted nor absorbed but are reflected from the surface.


Yuri Endo 2012

When the light hits mirror, the light reflects back in different direction at the same angle as the incident ray. ( The angle of incidence is equal to the angle of reflection

The amount of light that is reflected from a surface depends on the nature of the surface and the angle at which the light strikes the surface. 


Yuri Endo 2012

Total internal reflection occurs when the light is passing through a medium with higher refractive index to lower refractive index at the angle of incidence greater than the so-called critical angle.

For any angle of incidence larger than the critical angle, Snell's law does not apply for the angle of refraction. In that case, obeying the law of reflection, the light stops crossing the boundary surface and completely reflects back internally.

In this experiment using a semi-circular glass, the light is passing from the glass ( higher refractive index ) to air ( lower refractive index ). When the light is pointing towards the center of the flat face at certain angle ( the angle of incidence above the critical angle), it hits the curved surface but does not  refract at the boundary. This optical phenomenon would not occur when the light is passing from air  ( lower refractive index ) to the glass ( higher refractive index ).

Optical fibers and prismatic binoculars take advantages of this physical property. This is also what makes diamonds sparkle brighter than the rest ( Diamonds have unusually high reflective index).

Reference: Video: Law of Reflection

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