During the Investigation of a New Type of Optical Fiber $n = 1.21$

Multiple Choice

During the investigation of a new type of optical fiber having an index of refraction $n = 1.21$ ) , a laser beam is aimed at the flat end of a straight fiber, as shown in the figure. What is the maximum angle of incidence $\theta _ { 1 }$ if the beam is not to escape from the sides of the fiber if it is surrounded by air?

A) $36.7 ^ { \circ }$
B) $39.8 ^ { \circ }$
C) $30.5 ^ { \circ }$
D) $42.9 ^ { \circ }$
E) $33.6 ^ { \circ }$