Question

Define the critical angle and state the conditions required for Total Internal Reflection (TIR).

Hint:

TIR occurs only when light goes from denser to rarer medium and the angle of incidence exceeds the critical angle.

Answer 1

Concept: Total Internal Reflection (TIR) is a phenomenon in which a light ray is completely reflected back into the denser medium instead of refracting into the rarer medium. Definition of Critical Angle: The critical angle is the angle of incidence in the denser medium for which the angle of refraction in the rarer medium becomes \( 90^\circ \). \[ \text{At critical angle: } r = 90^\circ \] Mathematical expression: From Snell's law, \[ n_1 \sin C = n_2 \sin 90^\circ \] \[ \sin C = \frac{n_2}{n_1} \] where:
\( n_1 \) = refractive index of denser medium
\( n_2 \) = refractive index of rarer medium
Conditions for Total Internal Reflection (TIR):
The light must travel from a denser medium to a rarer medium. (\( n_1>n_2 \))
The angle of incidence in the denser medium must be greater than the critical angle. (\( i>C \))
Result: Under these conditions, the refracted ray disappears and the entire light is reflected back into the denser medium.