question_answer

Rakhi got a new diamond ring by her mother on her 18th birthday. She shared with her best friend Neelima and showed her the ring too. She amazed to see the brilliance of diamond and wanted to know the reason behind it. Neelima, than gave her brief explanation of her queries.

(i) Which two values are displayed by Neelima in responding to Rakhi's queries?

(ii) Three light rays, red (R), green (G) and blue (B) are incident on a right angled prism ABC at face AB. The refractive indices of the material of the prism for red, green and blue wavelengths are 1.39, 1.44 and 1.47, respectively. Out of the three, which colour of ray will emerge out of face AC? Justify your answer.

Light rays are incident on a right angled prism, ABC

 

Answer:

            (i) Readily sharing knowledge and good scientific attitude about various things.             (ii) Total internal reflection takes place on AC By geometry, angle of incidence (i) at face AC for all three rays is \[45{}^\circ .\] Light suffers total internal reflection for which this angle of incidence is greater than critical angle. \[i<{{i}_{c}}\]\[\Rightarrow \]\[\sin i>\sin {{i}_{c}}\] or         \[\sin 45{}^\circ >\sin {{i}_{c}}\] or \[\frac{1}{\sin 45{}^\circ }<\frac{1}{\sin {{i}_{c}}}\] Total internal reflection takes place on AC for rays with\[\mu >\sqrt{2}=1.414\] i.e. green and blue colour suffers Total Internal Reflection (TIR), whereas red undergoes refraction.