Physics-
General
Easy
Question
Light guidance in an optical fiber can be understood by considering a structure comprising of thin solid glass cylinder of refractive index 
surrounded by a medium of lower refractive index 
. The light guidance in the structure takes place due to successive total internal reflections at the interface of the media and as shown in the figure. All rays with the angle of incidence i less than a particular value im are confined in the medium of refractive index . The numerical aperture (NA) of the structure is defined as sin im .
For two structures namely S1 with 
and 
and 
and taking the refractive index of water to be 4/3 and that of air to be 1, the correct option (s) is (are)
- NA of
immersed in water is the same as that of 
immersed in a liquid of refractive index 
- NA of immersed in liquid of refractive index
is the same as that of 2 immersed in water
- NA of placed in air is the same as that of immersed in liquid of refractive index
- NA of placed in air is the same as that of placed in water
immersed in water is the same as that of immersed in a liquid of refractive index
immersed in liquid of refractive index is the same as that of 2 immersed in water
placed in air is the same as that of immersed in liquid of refractive index
placed in air is the same as that of placed in water
The correct answer is: NA of immersed in water is the same as that of immersed in a liquid of refractive index
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