© 2012 Pearson Education, Inc. { Chapter 32 Electromagnetic Waves (cont.)

© 2012 Pearson Education, Inc. Standing electromagnetic waves Electromagnetic waves can be reflected by a conductor or dielectric, which can lead to standing waves. (See Figure below.) Electromagnetic waves can be reflected by a conductor or dielectric, which can lead to standing waves. (See Figure below.) Mathematically, standing waves are a superposition of incoming and outgoing waves. Mathematically, standing waves are a superposition of incoming and outgoing waves.

© 2012 Pearson Education, Inc. The drawing shows a sinusoidal electromagnetic standing wave. The average Poynting vector in this wave Q32.8 A.points along the x-axis. B.points along the y-axis. C. points along the z-axis. D. is zero. E. none of the above

© 2012 Pearson Education, Inc. The drawing shows a sinusoidal electromagnetic standing wave. The average Poynting vector in this wave A32.8 A.points along the x-axis. B.points along the y-axis. C. points along the z-axis. D. is zero. E. none of the above

© 2012 Pearson Education, Inc. { Chapter 33 The Nature and Propagation of Light

© 2012 Pearson Education, Inc. The nature of light  Light has properties of both waves and particles. The wave model is easier for explaining propagation, but some other behavior requires the particle model.  The rays are perpendicular to the wave fronts ( cross sections of the wave which are in phase ).  This chapter will concentrate on the ray perspective

© 2012 Pearson Education, Inc. Reflection and refraction When light strikes a surface, it is (in general) both reflected and refracted.

© 2012 Pearson Education, Inc. Specular and diffuse reflection Specular reflection occurs at a very smooth surface (left figure). Specular reflection occurs at a very smooth surface (left figure). Diffuse reflection occurs at a rough surface (right figure). Diffuse reflection occurs at a rough surface (right figure). Our primary concern is with specular reflection. Our primary concern is with specular reflection.

© 2012 Pearson Education, Inc. Laws of reflection and refraction The index of refraction is n = c/v >1. The index of refraction is n = c/v >1. Angles are measured with respect to the normal. Angles are measured with respect to the normal. Reflection: The angle of reflection is equal to the angle of incidence. Reflection: The angle of reflection is equal to the angle of incidence. Refraction: Snell’s law applies. Refraction: Snell’s law applies. In a material = 0 /n. In a material = 0 /n. Figure 33.7 (right) illustrates the laws of reflection and refraction. Figure 33.7 (right) illustrates the laws of reflection and refraction.

© 2012 Pearson Education, Inc. Reflection and refraction in three cases Figure 33.8 below shows three important cases: Figure 33.8 below shows three important cases: If n b > n a, the refracted ray is bent toward the normal. If n b > n a, the refracted ray is bent toward the normal. If n b < n a, the refracted ray is bent away from the normal. If n b < n a, the refracted ray is bent away from the normal. A ray oriented along the normal never bends. A ray oriented along the normal never bends.

© 2012 Pearson Education, Inc. Why does the ruler appear to be bent? The straight ruler in Figure 33.9(a) appears to bend at the surface of the water. The straight ruler in Figure 33.9(a) appears to bend at the surface of the water. Figure 33.9(b) shows why. Figure 33.9(b) shows why.

© 2012 Pearson Education, Inc. Some indexes of refraction

© 2012 Pearson Education, Inc. Light passes from vacuum (index of refraction n = 1) into water (n = 1.333). If the incident angle  a is in the range 0° <  a < 90°, Q33.2 A. the refracted angle is greater than the incident angle. B. the refracted angle is equal to the incident angle. C. the refracted angle is less than the incident angle. D. the answer depends on the specific value of  a.

© 2012 Pearson Education, Inc. Light passes from vacuum (index of refraction n = 1) into water (n = 1.333). If the incident angle  a is in the range 0° <  a < 90°, A33.2 A. the refracted angle is greater than the incident angle. B. the refracted angle is equal to the incident angle. C. the refracted angle is less than the incident angle. D. the answer depends on the specific value of  a.

© 2012 Pearson Education, Inc. When light passes from vacuum (index of refraction n = 1) into water (n = 1.333), Q33.1 A. the wavelength increases and the frequency is unchanged. B. the wavelength decreases and the frequency is unchanged. C. the wavelength is unchanged and the frequency increases. D. the wavelength is unchanged and the frequency decreases. E. both the wavelength and the frequency change.

© 2012 Pearson Education, Inc. When light passes from vacuum (index of refraction n = 1) into water (n = 1.333), A33.1 A. the wavelength increases and the frequency is unchanged. B. the wavelength decreases and the frequency is unchanged. C. the wavelength is unchanged and the frequency increases. D. the wavelength is unchanged and the frequency decreases. E. both the wavelength and the frequency change.

© 2012 Pearson Education, Inc. Light passes from a medium of index of refraction n a into a second medium of index of refraction n b. The angles of incidence and refraction are  a and  b, respectively. If n a < n b, Q33.3  a >  b and the light speeds up as it enters the second medium. B.  a >  b and the light slows down as it enters the second medium. C.  a <  b and the light speeds up as it enters the second medium. D.  a <  b and the light slows down as it enters the second medium.

© 2012 Pearson Education, Inc. Light passes from a medium of index of refraction n a into a second medium of index of refraction n b. The angles of incidence and refraction are  a and  b, respectively. If n a < n b, A33.3  a >  b and the light speeds up as it enters the second medium. B.  a >  b and the light slows down as it enters the second medium. C.  a <  b and the light speeds up as it enters the second medium. D.  a <  b and the light slows down as it enters the second medium.

© 2012 Pearson Education, Inc. Total internal reflection Light striking at the critical angle emerges tangent to the surface. (See Figure below.) Light striking at the critical angle emerges tangent to the surface. (See Figure below.) If  a >  crit, the light is undergoes total internal reflection. If  a >  crit, the light is undergoes total internal reflection.

© 2012 Pearson Education, Inc. Some applications of total internal reflection A binocular using Porro prisms (below) and a “light pipe” (right) make use of total internal reflection in their design. A binocular using Porro prisms (below) and a “light pipe” (right) make use of total internal reflection in their design.

© 2012 Pearson Education, Inc. A diamond and a periscope Diamonds sparkle because they are cut so that total internal reflection occurs on their back surfaces. See Figure below. Diamonds sparkle because they are cut so that total internal reflection occurs on their back surfaces. See Figure below.

© 2012 Pearson Education, Inc. Dispersion Dispersion: The index of refraction depends on the wavelength of the light. See Figure (right). Dispersion: The index of refraction depends on the wavelength of the light. See Figure (right). Figure (below) shows dispersion by a prism. Figure (below) shows dispersion by a prism.