Question

The optical fibres have an inner core of refractive index $ {{n}_{1}} $ and a cladding of refractive index $ {{n}_{2}}, $ such that

• A. $ {{n}_{1}}={{n}_{2}} $
• B. $ {{n}_{1}}\le {{n}_{2}} $
• C. $ {{n}_{1}}<{{n}_{2}} $
• D. $ {{n}_{1}}>{{n}_{2}} $
• E. $ {{n}_{1}}\ge {{n}_{2}} $

Answer 1

Answer: (D)

Optical fibre is made of a thin glass core (diameter 10 to $ 100\text{ }\mu m $ ) surrounded by a glass coating called cladding is protected by a jacket of plastic. The refractive index of the glass used for making core $ ({{n}_{1}}\approx 1.7) $ is a little more than the refractive index of the glass $ ({{n}_{2}}=1.5) $ used for making the cladding ie, $ {{n}_{1}}>{{n}_{2}} $ .