Physics class 12th Reflection

Total Internal Reflection (TIR)




Total Internal Reflection (TIR) is a phenomenon in optics that occurs when a light ray traveling in a

denser medium

(like water or glass) hits the boundary with a less dense medium (like air) at an angle greater than a

certain

critical angle. Instead of refracting into the second medium, the light ray is completely reflected back

into

the denser medium.



Conditions for Total Internal Reflection:

1. Light travels from a denser medium to a less dense medium.

The refractive index of the first medium (n1) must be greater than that of the second medium (n2).

For example,

glass to air or water to air.

2. The angle of incidence exceeds the critical angle.

The critical angle (theta_c) is the angle of incidence beyond which all the light is reflected

internally. It is given by:

sin(theta_c) = n2 / n1

where:

- n1 = refractive index of the denser medium

- n2 = refractive index of the less dense medium



How It Happens:

1. At small angles of incidence (less than theta_c):

Part of the light is refracted into the second medium, bending away from the normal, and some is