Snell’s Law and Total Internal Reflection

    Theoretical Background When light travels between two different mediums, the velocity and wavelength changes. The result is the “bending” of the light. The “bending” of light is referred to as refraction. The “bending” follows a convenient mathematical relationship called Snell’s law, named after Dutch astronomer Willebrord Snellius (1580-1626). The purpose of this lab is to determine the relationship between the incident angle of a light beam and the refracted angle of the light beam as the beam passes from one medium to another. In addition, we will demonstrate an application of Snell’s Law by measuring the critical angle for a light beam that travels from a more dense medium to a less dense medium. Experimental Procedure Part I: Snell’s Law 1. Watch the Introductory video and follow instructions given. Below I give a step by step procedure that I use in the video. 2. Open link, this will bring you to a loading screen. Select the ‘More Tools’ icon. 3. Turn on the laser and drag the circular protractor such that the protractor is centered along the normal line and the boundary between the two mediums. Also, drag the speed indicator tool out from the tools located at the lower left of the simulation. The laser can be dragged to change the incident angle. Play with the simulation and try changing some of the different parameters. Make sure to select “Ray” and check the “Angles” box. 4. The index of refraction is given by the letter 𝑛𝑛, and is defined as the ration of the speed of light in a vacuum to the speed of light in the medium, 𝑛𝑛 = 𝑐𝑐 𝑣𝑣 , where 𝑐𝑐 = 3.0 × 108 𝑚𝑚 𝑠𝑠 . As light travels into different substances the velocity of light decreases. For our purposes the speed of light in a vacuum will be the same as that of air. Use the speed tool to measure the velocity of light in the glass. Write the velocity in terms of 𝑐𝑐. 5. Use the definition for the index of refraction to verify that the index of refraction for glass is 1.5. Show all your work. 6. The relationship between the velocity, frequency, and wavelength of a wave is given by 𝑣𝑣 = 𝜆𝜆𝜆𝜆. Since the frequency remains constant when light travels between different media, an expression can be written to solve for 𝜆𝜆2.