Lecture Outline Chapter 22 College Physics, 7 th Edition Wilson / Buffa / Lou © 2010 Pearson Education, Inc.

22.1 Wave Fronts and Rays Along a wave front, all the waves have the same phase. A wave front is the line or surface defined by adjacent portions that are “in phase” An easy way to think of this, is that each “wave front” separates wavelengths. © 2010 Pearson Education, Inc.

22.1 Wave Fronts and Rays Waves propagate outward from a source. Waves move at a certain speed and that speed is greatest in a vacuum. C = We use rays because it shows the direction of energy flow. © 2010 Pearson Education, Inc.

22.1 Wave Fronts and Rays Why do we see objects? Because rays from objects, or appearing to be from them, enter our eyes and converge where? Our brains cannot tell whether rays actually come from objects. This is one way magicians can fool our eyes! © 2010 Pearson Education, Inc.

22.2 Reflection The basic rule of reflection is that the angle of incidence equals the angle of reflection. Note that the angles are measured from the normal to the surface. © 2010 Pearson Education, Inc.

22.2 Reflection Let’s look at incident pulse, reflected pulse, angles of incidence and reflection, and the normal. Finally, Law of Reflection is…

22.2 Reflection Specular reflection is reflection from a smooth surface. In this case, incident rays are all parallel to one another, and reflected rays are parallel to one another. © 2010 Pearson Education, Inc.

22.2 Reflection Diffuse reflection is reflection from a rough surface. The reflected rays are not parallel. © 2010 Pearson Education, Inc.

22.2 Reflection Driving on a dry night vs. driving on a dark, rainy, night. Specular Reflection is a major cause of accidents on rainy nights.

22.2 Reflection Two mirrors are perpendicular to to each other, with a light ray incident on one the mirrors shown to the right. Sketch the path of the reflected ray. Find where the reflected ray would go. Let’s Draw This:

22.2 Reflection Reflected rays are drawn using © 2010 Pearson Education, Inc.

22.3 Refraction Refraction occurs because the speed of light is different in different media. As light travels across a boundary between media, it bends. Thus, there is a change in direction of a wave when the medium changes. The relationship between the angle of incidence and the angle of refraction is: © 2010 Pearson Education, Inc.

22.3 Refraction Again, the angles are measured from the normal to the surface. Direction of incident is different than the direction of the transmitted. © 2010 Pearson Education, Inc.

22.3 Refraction The index of refraction is the ratio of the speed of light in vacuum to the speed of light in the medium. The index of refraction is always equal to or greater than 1. The index of refraction is also a measure of optical density. Example…

22.3 Refraction The frequency of the wave stays the same, but the wavelength of the light is shorter where the index of refraction is greater. © 2010 Pearson Education, Inc. Let’s rearrange this please!

22.3 Refraction Light from a helium – neon laser with a wavelength of nm travels from air into water. What are the speed and wavelength of the laser light in water?

22.3 Refraction Snell’s law can be rewritten using the index of refraction: A ray bends toward the normal if the second medium has a larger index of refraction, and away from it if it is smaller. © 2010 Pearson Education, Inc.

22.3 Refraction Light in water is incident on a piece of crown glass at an angle of 37 degrees. –A) Will the transmitted ray be Bent toward the normal? Bent away from the normal? Not be bent at all? –B) What is the angle of refraction?

22.3 Refraction A simplified representation of the crystalline lens in a human eye shows it to have a cortex (outer layer) on n = and a nucleus (core) of n = –If a beam of monochromatic light of wavelength 590 nm is directed from air through the front of the eye and into the crystalline lens, calculate the frequency, speed, and wavelength of light in the cortex and in the nucleus.

22.3 Refraction A beam of light traveling in air strikes the glass top of a coffee table at an angle of incidence of 45 degrees. The glass has an index of 1.5. What is the angle of refraction for the light transmitted into the glass? © 2010 Pearson Education, Inc.

22.3 Refraction Mirages are formed by light refracting through air of different temperatures (and therefore densities). © 2010 Pearson Education, Inc.

22.3 Refraction Refraction can distort underwater views, make straight objects appear bent, and make submerged objects appear shallower than they really are. © 2010 Pearson Education, Inc.

22.3 Refraction Refraction through the atmosphere can make the Sun appear flattened at sunset, and increase the length of the day. © 2010 Pearson Education, Inc.

22.4 Total Internal Reflection and Fiber Optics There’s a limit of how far the refracted ray can bend. If the incident angle is large enough (critical angle), the angle of refraction is 90 degrees, at this angle of larger, light is no longer refracted, but it is internally reflected. Total Internal Reflection © 2010 Pearson Education, Inc.

22.4 Total Internal Reflection and Fiber Optics The angle for which this occurs is called the critical angle: Light impinging on the boundary at this or a larger angle will be reflected; this is called total internal reflection. © 2010 Pearson Education, Inc.

22.3 Refraction What is the critical angle for light traveling in water and incident on a water-air boundary? Imagine a beautiful beachy scene…

22.4 Total Internal Reflection and Fiber Optics © 2010 Pearson Education, Inc.

22.4 Total Internal Reflection and Fiber Optics Fiber optics use total internal reflection to guide light along the fiber. The reflection means that there are no losses out the sides of the fiber. Low energy losses, not affected by electromagnetic disturbances, can change light energy into electrical energy – used in phone and computer lines. © 2010 Pearson Education, Inc.

22.5 Dispersion Dispersion occurs because the index of refraction depends slightly on wavelength. White light is composed of all colors. Dispersion varies with different media. © 2010 Pearson Education, Inc.

22.5 Dispersion The index of refraction of a particular transparent material is (640 nm) for the red end of the visible spectrum and (434 nm) for the blue end. White light is incident at an angle of 45 degrees. Inside the prism, the angle of refraction of the red light is: larger than, smaller than, or the same as the angle of refraction of the blue light? What is the angular separation of the visible spectrum inside the prism? © 2010 Pearson Education, Inc.