A cylinderical optical fibre (quarter circular shape) of refractive in – McqOptions

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1.	A cylinderical optical fibre (quarter circular shape) of refractive index \[n=2\] and diameter \[d=4\text{ }mm\] is surrounded by air. A light beam is sent into the fibre along its axis as shown in figure. Then the smallest outer radius R (as shown in figure) for which no light escapes after first incident on curved surface of fibre is:
A.	2 mm
B.	4 mm
C.	8 mm
D.	6 mm
Answer» C. 8 mm

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