LECTURE 11 REFLECTION & REFRACTION, Exercises of Law

Download LECTURE 11 REFLECTION & REFRACTION and more Exercises Law in PDF only on Docsity! LECTURE 11 REFLECTION & REFRACTION Instructor: Kazumi Tolich Lecture 11 ¨ Reading chapter 31-3 ¤ Reflection ¤ Refraction ¤ Dispersion 2 Snell’s law ¨ The angle of transmitted ray, θ2, is called angle of refraction. ¨ The angles of incidence and refraction, and indices of refraction of two media are related by Snell’s Law: 𝑛" sin𝜃" = 𝑛) sin𝜃) ¤ In a medium in which light slows down, a ray bends closer to the normal. 5 Demo 2 ¨ Refraction and Reflection from Plastic Block ¤ Demonstration of Snell’s law: the ray bends closer to the normal in the plastic. ¤ 𝑛" sin 𝜃" = 𝑛) sin 𝜃) 6 Quiz: 1 Specular reflection ¨ Reflection from a smooth surface is called specular reflection. ¨ After reflection, the rays diverge exactly as if they came from a point P’ called the image point. 10 Demo 3 ¨ Location of Image (candle in glass of water) ¤ Demonstration of image point. 11 Diffuse reflection ¨ When light reflects off a rough surface, diffuse reflection, the rays from a point reflect in random directions and do not diverge from any point, failing to form any image. ¨ Light reflected off a dry street is a diffuse reflection, but light reflected off a wet street becomes more specular, and it makes difficult to see what is on the road. 12 Example 2 ¨ 16 % of light energy is reflected from an air-diamond interface at normal incidence. How fast does light travel in diamond? 15 n1 n2 Total internal reflection ¨ When the incident light is in a medium with a higher index of refraction, the angle of refraction is greater than the incident angle. ¨ For incident angles greater than the critical angle, and no refracted ray exists. This phenomenon is called total internal reflection. The critical angle, θc, is given by 𝜃* = sin+" 𝑛) 𝑛" 16 Binoculars ¨ If the index of refraction of the glass is typical 1.5, the critical angle for total internal reflection is 41.8º. ¨ If the angle of incidence of the ray on the glass–air interface is 45º, the light will be totally reflected. ¨ In binoculars, two prisms are used on each side. 17 Glass prism FlipItPhysics-8: Swimming Pool ¨ Can the person standing on the edge of the pool be prevented from seeing the light by total internal reflection at the water-air surface? ¨ No! The ray that makes smaller incident angle still makes out of water. 20 Example 3 ¨ A light bulb is set in the bottom of a 3.0 m deep swimming pool. What is the diameter of the pool’s surface where the light can escape? 21 h = 3.0 m Mirages ¨ The speed of light wave is slightly greater in the less dense layer of hot air near the pavement, so a light beam passing from the cooler layer into the warmer layer is bent. 22 Uniform temperature Hot near the ground Quiz: 2 Quiz 11-2 answer ¨ Which of the following statements is true about the speeds of the various colors of light in glass? ¨ Red has the highest speed, violet the lowest. ¨ The red light bends least, so the speed of red light is closest to the speed of light in air. Quiz: 3