Question

White light is incident on the interface of glass and air, as shown in the figure. If green light is just totally and internally reflected, then the emerging ray in air contains :

• A. all colours
• B. yellow, orange and red
• C. violet, indigo and blue
• D. all colours except green

Answer 1

Answer: (B)

Critical angle ${{\theta }_{C}}={{\sin }^{-1}}\left( \frac{1}{\mu } \right)$ wavelength increases in the sequence of VIBGYOR. According to Cauchys formula refractive inde $(\mu )$ decreases as the wavelength increases. Hence, the refractive index will increase in the sequence of ROYGBIV. The critical angle ${{\theta }_{C}}$ will thus increase in the same order VIBGYOR. For green light the incidence angle is just equal to the critical angle. For yellow, orange and red the critical angle will be greater than the incidence angle. So, these colours will emerge from the glass air interface.