"During refraction of light through the glass slab, incident ray and emergent ray are parallel to each other." Explain.

If the angle of incidence and angle of emergence of a light ray falling on a glass slab are given then by applying snell’s law we can get

$\frac{\sin i}{\sin r}=\frac{n_2}{n_1}$

When the light travels from the air to glass

$\frac{\sin i}{\sin r}={\mu }_g^a$

Now the light travels withing the glass the angle of incidence is equal to the angle of reflection

When light goes out of the glass into air then according to snells law

$\frac{\sin r}{\sin e}=\frac{n_1}{n_2}$

$\frac{\sin r}{\sin e}={\mu }_a^g$

On multiplying the above two equation we get

$\frac{\sin i}{\sin e}=1$

$\sin i=\sin e$

$i=r$

Hence the angle of incidence is equal to the angle of emergence and the rays are parallel to each other.