Question

Explain total internal reflection using diagram.

Answer 1

When an oblique ray of light travels from optically denser medium to an optically rarer medium, it bends away from the normal at the surface separating the two media.

$\bullet$ According to Snells law, the angle of refraction increases with the increase in the angle of incidence. The figure below shows refraction between two media.

$\bullet$ As shown in the figure above, the rays $A{B}_2$ and $A{B}_3$ originating from Point $A$ of the source undergoes partial refraction and partial reflection.

$\bullet$ The refracted ray for the incident ray $A{B}_4$ travels along the surface separating the two media. So, its angle of refraction is ${90}^{\circ }$.

$\bullet$ When a ray of light travels from the denser medium to the rarer medium, the angle of incidence for which the angle of refraction is ${90}^{\circ }$ is known as the critical angle.

$\bullet$ When the angle of incidence exceeds the critical angle, the ray is totally internally reflected. This is the phenomenon of total internal reflection.