Question

One side of a glass slab is silvered as shown in the figure. A ray of light is incident on the other side at an angle of incident of ${45}^{\circ }$. Refractive index of glass is $\sqrt{2}$. The deflection suffered by the light ray when it comes out of slab will be

• A. ${75}^{\circ }$
• B. ${90}^{\circ }$
• C. ${60}^{\circ }$
• D. ${45}^{\circ }$

Answer 1

The correct option is B ${90}^{\circ }$

On drawing a ray diagram of the given situation based on law of symmetry and laws of reflection and refraction.


We can see that,
$\angle B=\angle A={45}^{\circ }$ $[$ alternate angle$]$
Applying Snell's law and law of reflection, $\angle C={45}^{\circ }$
So, in $△BCD$,
$\angle B+\angle C+\angle D={180}^{\circ }$
$\Rightarrow {45}^{\circ }+{45}^{\circ }+\delta ={180}^{\circ }$
$\Rightarrow \delta ={90}^{\circ }$
$[$anticlockwise$]$

Why this question? It challenges you to apply the fundamental concept of reflection, refraction and deviation of a light ray.