Question

A glass prism is immersed in a hypothetical liquid. The curves showing the refractive index $n$ as a function of wavelength $\lambda$ for glass and liquid are as shown in the figure. When the ray of white light is incident on the prism parallel to the base:

• A. yellow ray travels without deviation
• B. blue ray is deviated towards the vertex
• C. red ray is deviated towards the base
• D. there is no dispersion

Answer 1

Answer: (A), (B), (C)

The correct options are
A yellow ray travels without deviation
B blue ray is deviated towards the vertex
C red ray is deviated towards the base



a)Yellow ray travels undeviated, because $n_L=n_g$
b) ${\lambda }_b<{\lambda }_y$. To the left of ${\lambda }_{yellow}$, $n_L>n_g$. Hence the ray will bend away from the normal,blue ray is deviated towards the vertex.
c) ${\lambda }_r>{\lambda }_y$. To the right of ${\lambda }_{yellow}$ in graph $n_L<n_g$. Hence the ray will bend towards the normal, red ray is deviated towards the base.