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?