Question

The refractive index of a liquid is 5/3. A Ray of light travelling in this liquid falls at interface of liquid and air. At what angle of incidence should it fall on liquid-air interface so that it suffers a total internal reflection?

Answer 1

1. We know that for total internal reflection a light ray should be moving from denser to rarer medium.
2. Also the angle of incidence must be greater than critical angle ($i_c$ ).
3. Critical angle is the angle of incidence for which angle of the reflection is ${90}^o$ .

By Snell's law, we know that

$\mu =\frac{1}{\sin i_c}$ (where $\mu$ is refractive index)

$\sin i_c=\frac{1}{\mu }$

$\sin i_c=\frac{3}{5}$

$i_c={37}^o$

Therefore, for total internal reflection angle of incidence should be more than

${37}^o$

.