Optics 2 Question 19
19. A ray of light travelling in a transparent medium falls on a surface separating the medium from air at an angle of incidence $45^{\circ}$. The ray undergoes total internal reflection. If $n$ is the refractive index of the medium with respect to air, select the possible value (s) of $n$ from the following
(1998, 2M)
(a) 1.3
(b) 1.4
(c) 1.5
(d) 1.6
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Answer:
Correct Answer: 19. (c, d)
Solution:
- For total internal reflection to take place Angle of incidence, $i>$ critical angle, $\theta _c$
or $\sin i>\sin \theta _c$ or $\sin 45^{\circ}>1 / n$
or $\quad \frac{1}{\sqrt{2}}>\frac{1}{n}$ or $n>\sqrt{2}$ or $n>1.414$
Therefore, possible values of $n$ can be 1.5 or 1.6 in the given options.
