Optics Guided Notes
Name:__________________ Class:_______
Do Now
Draw a reflected sound wave, labeling the angle of incidence and the angle of reflection.
How do these angles compare?
Draw the wave fronts of a light wave passing through three different media.
The first medium be medium speed
The second should be faster speed
The should be slow speed
Your picture should show realistic angles of refraction and changes in wave length.
Index of Refraction
The index of refraction (n) is a value that describes the __________________________________________
______________________________________.
n = index of refraction, has no units
c = speed of light in a vacuum, 3.00 X 108 m/s
v = speed of light in a particular medium
Since c is the fastest speed of light, n is always greater than 1.
The larger the index the _______________ the speed in that medium .
The greater the difference in n, the ______________________ the angle
of refraction.
Total Internal Reflection
Critical angle: qc ____________________________________________________________________________________
Application: Fiber Optics
A fiber optic cable is a _____________________________________________________________________________
__________________________________________________________________________________________________.
 Critical angle is very small  almost everything is totally internally reflected.
 The light is guided through the cable by successive internal reflections with almost no loss (a little escapes).
 Even if the light pipe is bent into a complicated shape (tied into knots), light is transmitted practically undiminished to
the other end.
Why use fiber optics?
 ___________________________________________________________________________________________
___________________________________________________________________________________________
 One single optical fiber can transmit several TV programs and tens of thousands of telephone conversations, all
at the same time.
 takes 300 lbs of copper to carry same info as 1 lb of fiber optics
 Downside: expensive
Dispersion
Even though all colors of the visible spectrum travel with the same speed in vacuum, the speed of the colors of the
visible spectrum varies when they pass through a transparent medium like glass and water. That is, the refractive index
of glass is different for different colors.
Different colors (frequencies) are refracted by different amounts! True for different pitches, as well!
Diffraction
When waves pass through a small opening, or pass the edge of a barrier, they always spread out to some extent into the
region that is not directly in the path of the waves.
_______________________________________________________________________ obstruction is called diffraction.
Diffraction effects are greater when the wavelength is big relative to the size of the obstruction.
__________________________________________________________ = noticeable diffraction
Diffraction explains why we can hear but not see around corners and other obstructions...
Wavelengths of audible sound: 16.7 mm – 16.7m
Wavelengths of visible light:
400 nm – 700 nm
Audible ___________________________________________are around the same size, or even bigger, than most
obstructions (open doorway, side of a building, etc.), so they ___________________________________.
Visible _____________________________ are much much smaller than these obstructions, and so they ____________
_____________________________________________________________.
Why do dolphins, bats, SONAR, and doctors use ultrasound for localizing objects, instead of lower frequency sounds?