L9. Total Internal Reflection - Lesson PDF

Total Internal Reflection Angle of Refraction In order for light to refract, the rays must be coming into a medium at an angle. When light rays hit a medium at 90°, there is no refraction. Angle of Refraction Light bends away from the normal when travelling from a more dense medium to a less dense...

Total Internal Reflection Angle of Refraction In order for light to refract, the rays must be coming into a medium at an angle. When light rays hit a medium at 90°, there is no refraction. Angle of Refraction Light bends away from the normal when travelling from a more dense medium to a less dense medium. In this situation, the angle of refraction is always larger than the angle of incidence. θR θi Critical Angle The angle of refraction continues to increase as the angle of incidence increases. Eventually, the angle of refraction will become 90°. The angle of incidence at this point is called the critical angle. Total Internal Reflection If the angle of incidence is past the critical angle, the refracted ray will no longer exit the medium, but instead, reflect back into it. This phenomenon is called total internal reflection → when the angle of incidence is greater than the critical angle. Total Internal Reflection Total internal reflection occurs when these 2 conditions are met: 1. Light is travelling more slowly in the first medium than in the second medium. 2. The angle of incidence is large enough that no refraction occurs in the second medium. Instead, the ray is reflected back into the first medium. Check this out! Fibre Optics The laser and pop bottle video demonstrates a useful application of total internal reflection → fibre optics! used in the communications industry for phones, computers, and TVs. automotive industry uses optical fibres to transmit light to the instrument panel in cars. medical professionals use fibre optic technologies to see into parts of the human body (endoscope) Diamonds One of the features that make diamonds so attractive in jewelry is the fact that they sparkle. Diamonds have a high refractive index which means they have a very small critical angle of 24.4°. The small angle allows a great deal of incident light to undergo total internal reflection. This causes the “sparkling” effect we see in diamonds!  Practice 1. When is light travelling at its fastest? 2. Under what conditions can you slow down light and speed it up again? 3. Describe how light changes its direction when moving from one medium to another 4. What property of a medium is given by its index of refraction? 5. Through which medium does light pass more quickly, one with a refractive index of 2.0 or one with a refractive index of 3.0? 6. What is internal reflection? When does it occur?  Solutions 1. In a vacuum 2. Various materials; ie into water, then into glass 3. Can refract towards or away from normal or reflect back into medium 4. Index of refraction = how dense a material is 5. Faster in the 2.0 (smaller number = closer to speed in a vacuum at 1.0) 6. When an incident ray in a dense medium attempts to exit the material at an incident angle greater than the critical angle. The incident ray follows the rules of reflection and stays in the first medium.