Lesson+35+&+36

**﻿Advancememt in Physics @ Dwight Englewood** **Director: Elise Burns** **TA: Sebastian Luhol**

**1. Total internal reflection**
 * Total internal reflection is the total amount of incident light at the boundary between two media
 * There are 2 rules for internal reflection. First, the light must be in the more dense medium and approach the less dense medium
 * Second, the angle of incidence is greater than the critical angle
 * But the angle of incidence must be large and the maximum angle of refraction is 90 degrees and the angle of incidence must be greater than 48.6 degrees to have total internal refraction occur

**2. Critical Angle**
 * The critical angle is the angle of incidence value
 * But, when you look at the critical angle, the actual value of the angle depends on the combination of materials present on each side of the boundary
 * To calculate the critical angle, you must take the inverse sine of the ratio of the indices of refraction
 * **equation:** critical angle= sin-1(nr/ni) index of refraction

**3. Angle of deviation**
 * The angle of deviation is the angle made between the incident ray of light entering the 1st face of the prism and the refracted ray that emerges from the 2nd face of the prism because of the different indices of refraction, the angle of deviation varies with wavelength.

**4. Dispersion**
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">ROYGBIV- The light refracts towards the normal when entering the glass and away from the normal upon exiting the glass
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">The violet wavelength refracts more than the red
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">When the light is exiting the prism, the light goes the opposite direction
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">There is no overall angle of deviation for the different colors of white light
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">There is a thin red fringe present on one end of the beam and thin violet fringe present on the opposite side of the beam
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">The fringe represents the dispersion
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">Then you can see the dispersion shows the spectrum of wavelengths present in visible light

<span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">**5. Rainbow (ROYGBIV)** <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">**6. Mirage**
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">A rainbow can be a complete circle
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">There is a circle because there is a collection of droplets in the atmosphere that are capable of concentrating the dispersed light at angles of deviation of 40-42 degrees relative to the original path of light from the sun
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">The droplets form a circular arc and they disperse light and reflect it back towards the observer
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">Each drop refracts and disperses to the entire visible light spectrum [[image:http://images.dpchallenge.com/images_challenge/0-999/474/800/Copyrighted_Image_Reuse_Prohibited_316337.jpg width="126" height="167"]]
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">Red is refracted at a steeper angle and blue at a less steep angle
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">A mirage is an optical phenomenon that creates the illusion of water and makes the refraction of light through a non-uniform medium
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">You can see a mirage when it’s a sunny day and you are driving
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">It looks like there is a puddle far ahead and when you get there, you don’t see it
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">When there is less optically dense air, light is traveling downward and speeds up
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">The change in speed causes a change of direction
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">The light ray bends away from the normal, the ray would bend parallel to the roadway and bends upward toward the cooler [[image:http://dickinsonn.ism-online.org/files/2010/04/refraction-by-Moh_Tj-on-flickr-300x214.jpg width="300" height="214"]][[image:sophies-physics:pencil.JPG caption="pencil.JPG"]]

<span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">**7. Converging and diverging lens**
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">A converging lens is a lens that converges rays of light that are traveling parallel to its principal axis
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">You can tell when a lens is converging because they are thick across the middle and thin at the upper and lower edges
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">A diverging lens is a lens that diverges rays of light that travel parallel to its principle axis
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">They are thin across the middle and thick at the upper and lower edges
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">[|Lenses Demo]

<span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">**8. Double convex and concave lenses**
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">A double convex lens is symmetrical across both its horizontal and vertical axis because of the thicker middle, converge rays of light travel parallel to its principal axis
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">A double concave lens is symmetrical across its horizontal and vertical axis
 * <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">Since the concave lens is thinner at the middle, it will diverge rays of light that travel parallel to its principal axis.

<span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">**9. Converging lenses and characteristics** <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">There are 3 rules for a converging lens <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">__a.__ any incident ray traveling parallel to the principal axis of a converging lens will refract through the lens and travel through the focal point on the opposite side of the lens <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">__b.__ any incident ray traveling through the focal point on the way to the lens, will refract through the lens and travel parallel to the principal axis <span style="color: #ff0052; font-family: Tahoma,Geneva,sans-serif; font-size: 110%;">__c.__ an incident ray that passes through the center of the lens will continue in the same direction when it entered the lens.