PHYSICS · Single correct · CBSE · Physics · Ray Optics and Optical Instruments · Ray Optics and Optical Instruments
Problem
In a certain optical fibre, ncore=1.50 and nclad=1.48. A light ray inside the straight fibre strikes the core–cladding interface at an angle of 82∘ (measured from the normal), ensuring guidance. The fibre is then sharply bent so that at the bend the same ray now meets the interface at an angle of 74∘. What happens to this ray at the bend?
(a) It continues to undergo total internal reflection inside the core.
(b) It reflects partially at the interface and re-enters the core with diminished intensity.
(c) It refracts into the cladding, so the guided power is lost.
(d) It is completely absorbed at the core–cladding boundary and converts to heat.