Question

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

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

Answer 1

Answer: (A)

Critical angle ${\theta }_C=si{n}^{-1}\left(\frac{1}{\mu }\right)$
Wavelength increases in the sequence of VIBGYOR.
According to Cauchy's formula refractive index $(\mu )$
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.
Hence, the correct option is (a).