Talha's Physics Academy
Geometrical Optics - Total Internal Reflection & Optical Fibers
Define critical angle and total internal reflection.
Critical Angle
"The angle of incidence in a denser medium for which the angle of refraction in the rarer medium becomes exactly $90^\circ$ is called the critical angle."
If the angle of incidence is increased further beyond the critical angle, refraction ceases entirely, and all the light is reflected back into the denser medium.
Figure: Ray diagram showing critical angle ($r = 90^\circ$) and total internal reflection.
Total Internal Reflection (TIR)
"When light rays travel from a denser medium to a rarer medium and the angle of incidence exceeds the critical angle, the light rays are completely reflected back into the first medium instead of refracting. This phenomenon is called Total Internal Reflection."
Explain the telecommunication through optical fibers.
Telecommunication Through Optical Fibers
Optical fibers consist of ultra-thin, hair-sized threads made of flexible glass or plastic that transmit light signals over long distances with minimal loss.
Structure of an Optical Fiber:
- Core: The inner cylindrical part made of glass or plastic possessing a high refractive index.
- Cladding: The outer concentric coating surrounding the core, made of a material with a lower refractive index.
Working Principle: When a light ray enters the core at an appropriate angle and strikes the core-cladding boundary, the angle of incidence is greater than the critical angle. Consequently, the light undergoes repeated total internal reflection along the inside of the fiber. Even when the optical fiber cable is bent or curved, light continues to bounce internally without escaping, allowing signals to travel massive distances across global telecommunication networks without significant energy loss.
Figure: Working of Optical Fibers.
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