question_answer 16)

(a) Following figure shows a cross-section of a 'light pipe? made of glass fibre of refractive index 1.68. The outer covering of the pipe ismade of material of refractive index 1.44. Whatis the range of the angles of incident rays withthe axes of the pipe for which the total internalreflection inside the pipe take place as shownin the figure ? (b) What is the answer if there is no outercovering of pipe ?  

Answer:

(a) The maximum value of the acceptanceangle is given by where is the refractive index of core andthat of the cladding. Here   and. Therefore, the range of angle of incidence is (b) In case there is no outer coating, then = 1 (for air)        critical angle for reflection Now for   or Using Clearly,     Therefore, all incident rays in the range 0 to99° suffer total internal reflection.