question_answer

When the rectangular metal tank is filled to the top with an unknown liquid, as observer with eyes level with the top of the tank can just see the comer E; a ray that refracts towards the observer at the top surface of the liquid is shown. The refractive index of the liquid will be

A) 1.2                               

B) 1.4

C) 1.6                               

D) 1.9

Correct Answer: A

Solution :

Light ray is going from liquid (denser) to air (rarer) and angle of refraction is\[90{}^\circ \], so angle of incidence must be equal to critical angle from figure \[\sin \,C=\frac{4}{5}\] Also \[\mu \,\,=\,\,\frac{1}{\sin \,C}\,\,=\,\frac{5}{4}\,\,\,=\,\,1.2\]