Question

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

• A. 1.3
• B. 1.4
• C. 1.5
• D. 1.6

Answer 1

Answer: (D)

1.6

Answer 2

For total internal reflection to take place Angle of incidence, i > critical angle, $\theta_C$ $or\, \, \, \, \, \, sin i > sin \theta_C or sin 45^\circ > 1/n$ $or\, \, \, \, \, \, \frac{1}{\sqrt{2}} > \frac{1}{n}\, or\, n\, > \sqrt{2}\, or\, n\, > 1.414$ Therefore, possible values of n can be 1.5 or 1.6 in the given options.