Application of reflected and refracted light

In this lesson, we will learn:

• The total internal reflection conditions
• Solving problems on total internal reflation
• Formation of Mirage
• Dispersion of light
• The use of optical fibers

• Total Internal Reflection:
  
  Complete reflection, there is NO refraction
  It occurs under the following circumstances:


1. The ray of light travels from a more optically dense medium to a less optically dense medium.
2. The angle of incidence is greater than a certain limiting angle (the critical angle).

• Critical Angle
  
  The incident angle that causes the refracted ray to lie right along the boundary of the substance, angle $\theta _{c}$, is it unique to the substance.
  
  In other words;
  The measure of angle of incidence when angle refraction is 90°
  OR
  The measure of angle of incidence when the refracted ray grazes the boundary.
  
  < $r$ = 90° $\Rightarrow$ <$i$ = < $\theta _{c} \qquad$ Reflection and Refraction 

• The angle of incidence is greater than the critical angle; the ray of light is totally reflected, No refraction

• The angle of incidence is smaller than the critical angle; the ray of light gets both reflected and refracted.

• Effect of refraction and reflection: Mirage, Dispersion of light, and Optical fiber


• Mirage:
  An optical effect that is seen above the hot road, the road looks like a pool or mirror due to the total internal reflection of light.
  The layers of air above the ground are colder and less dense
  Layers at the surface of the ground are hotter and denser
  As light travels from less dense to denser layer with an angle of incidence greater than the critical angle, it gets totally reflected, no refraction

• Optical Fiber: It is a long thin flexible sample of a transparent medium. Any light ray entering the optical fiber will remain trapped inside, even if the fiber is bent.
  The total internal reflection occurs.
  Light energy stays the same throughout the fibers.
• Use of optical fibers
  1. Surgical tools to treat illness, without deterioration of image quality
  2. Telecommunication, to transfer video and audio information with no loss of signals.