Previous Year Question
“Endoscope” used by Doctors for examining the inside of the patient's stomach, works on the principle of
reflection of light
dispersion of light
total internal reflection of light
refraction of light
Correct Answer: C
Detailed Solution
A conventional fibre-optic endoscope uses optical fibres to carry light into the body and to transmit light or an image back from the internal region being examined.
An optical fibre consists of a core having a higher refractive index than the surrounding cladding. Light travelling through the core at an appropriate angle undergoes repeated Total Internal Reflection at the core-cladding boundary. This allows light to travel through a curved optical fibre with relatively low loss.
There are two principal conditions for Total Internal Reflection—light must travel from an optically denser medium towards a rarer medium, and the angle of incidence must be greater than the critical angle.
An endoscopic fibre bundle can therefore carry light to internal parts of the body that cannot be viewed directly. One fibre system may provide illumination while another carries the reflected light/image back to the observer.