Refraction of Light ------------------------------------ Joseph F. Alward, PhD Department of  Physics University of the Pacific

Applets in this eLecture: A FishEye's View of the World Internal Reflection Applet Dispersion through Slab of Glass Dispersion through Prism

 Ratio of Speed of Light in
 Vacuum to Speed in Various
 Substances                 (l = 589 nm )            

Substance	c/v	Substance	c/v
Diamond	2.419	Ethyl Alcohol	1.361
Cubic Zirconia	2.21	Ice	1.309
Glass (flint)	1.66	Water	1.333
Glass (crown)	1.52	Air	1.000

Index of Refraction

n = c/v  The larger the index,   the smaller the speed of   light

  Index of Refraction                

Substance	Index of Refraction       n	Substance	Index of Refraction       n
Diamond	2.419	Ethyl Alcohol	1.361
Cubic Zirconia	2.21	Ice	1.309
Glass (flint)	1.66	Water	1.333
Glass (crown)	1.52	Air	1.000

  Reflection and Refraction at an Interface                    

   Refraction:  The Bending of Wavefronts                     

One side of wave front slows down, and the entire train of fronts twists. Analogy: right front tire of vehicle enters mud, twisting vehicle to the right.

   Refraction Rules                                                                                      

Light twists inward when entering medium    of higher index of refraction

Light twists outward when entering medium    of lower index of refraction

  Understanding Refraction                                                                        

Above: Wheels on axle rolls along a smooth  sidewalk and onto grass. Which picture  path is followed?  What happens if the  motion is reversed? Right:  One side of wave front slows down, and the entire train of fronts twists.

   Illustrating Cart Analogy                                             

Right front wheel slows           Left front wheel slows   down before left front             down before right front

  Law of Refraction:  Snell's Law                     

Right front wheel slows down first.

Snell's Law:     n2 sin q2  =    n1 sin q1

   Snell's Law Example                                                 

n1 = 1.0 (air)   n2 = 1.52 (glass) q1 = 30 degrees ------------------------ n2 sin q2     =    n1 sin q1 1.52 sin q2 = 1.0 sin 30         sin q2 = 0.33 Put calculator in Mode Degree q2 = sin-1 (0.33)      = 19.3 degrees

  Rear View Mirror                             

  Rear View Mirror Explained                                         

  Apparent Depth in Water                                                       

Light exits into  medium (air)  of lower index  of refraction,  and turns left.

  More Apparent Depth                                                                                

Spear-fishing is made more difficult by the bending of light. To spear the fish in the figure, one must aim at a spot in front of the fish

  Refraction at Sunset                                                                                 

Why does the sun appear to be flattened at sunset? --------------------------------------------------- The sun actually falls below below the horizon, i.e., it "sets", a few seconds before we see it set.

 A Fish-Eye's View     

                                                      

A FishEye's View of the World (Excellent applet illustrating refraction)

 Water on Road Mirage                                

There's no water on the road; why does it appear so?

  The Oasis Mirage                                                  

   Displacement through a Slab of Glass                               

Entering and exiting rays are displaced  from each other, but parallel.

   Internal Reflection                                              

All rays reflect internally, but  the top three rays reflect only  a small percentage internally;  most energy leaves the prism.    The fourth and fifth rays are  reflected 100 % internally.

  Internal Reflection                                                        

Ray 4 is the first to be 100 % reflected; it's angle of incidence is called the critical angle.

  Crictical Angle Calculation                          

What must be q1 to get q2 = 90 deg ?

Snell's Law:  n1 sin q1 =  n2 sin q2               =  n2 sin 90     sin q1  =  n2 / n1 ------------------------------ Assume water to air:    n1 = 1.33              n2 = 1.00 q1  = sin-1 (0.752)     = 48.8 degrees qc = critical angle        = 48.8 degrees

 Cone of Light                                                                             

Crictical angle for water = 48.8 degrees  Light within the 48.8 degree cone  is detected by fish, while nothing in the  air outside that  cone can be seen.  The only light reaching the fish outside  the cone is that light (not shown) which  is reflected off the bottom of the pool.

Internal Reflection Applet

  Critical Angle of Diamond                           

n = 2.419 qc = sin-1(1.00/2.419)     = 24.42 degrees 90.00 - 24.42 = 65.58 degrees Light outside of 65.58 degree cone is reflected back inside. Virtually all light entering the top face of the diamond is reflected internally.

  Optical Fiber                                                                  

  Optical Fiber                                             

  Optical Fibers in Medicine                                                                                  

Arthroscopic Surgery                              Bronchoscope                                 Colonoscope

  Index of Refraction vs Color           

v = c/n The speed of blue light is less than the speed of red light. Blue light bends more than red light.

 The Spectrum of White Light                                           

Note that the shorter wavelengths of light are bent more than the longer; blue more than red.

   Applets

1. Dispersion through Slab of Glass 2.  Dispersion through Prism

 Refraction in a Raindrop                                                        

  Forming a Rainbow                                    

  Rainbow                                           

  Index Matching