Question

A ray of light travelling inside a rectangular glass block of refractive index $\sqrt{2}$ is incident on the glass-air surface at an angle o incidence of ${45}^o$.The refractive index of air is one. Under these conditions the ray will

• A. emerge into the air without any deviation
• B. be reflectived back into the glass
• C. be absorbed
• D. emerge into the air with an angle of refraction equal to ${90}_o$

Answer 1

The correct option is D emerge into the air with an angle of refraction equal to ${90}_o$

Using Snell's law:

${\mu }_i\sin \left(i\right)={\mu }_r\sin \left(r\right)$

$\Rightarrow \sqrt{2}\sin \left(45\right)=\sin \left(r\right)\therefore r=90$

therefore, the ray will emerge into air at ${90}^0$ , this angle of incidence is called as critical angle.