Chapter 32

1. Chapter 32 Electromagnetic Waves (cont.)

2. Electromagnetic waves can be reflected by a conductor or dielectric, which can lead to standing waves. (See Figure 32.22 below.) • Mathematically, standing waves are a superposition of incoming and outgoing waves. Standing electromagnetic waves

3. Q32.8 The drawing shows a sinusoidal electromagnetic standing wave. The average Poynting vector in this wave points along the x-axis. points along the y-axis. C. points along the z-axis. D. is zero. E. none of the above

4. A32.8 The drawing shows a sinusoidal electromagnetic standing wave. The average Poynting vector in this wave points along the x-axis. points along the y-axis. C. points along the z-axis. D. is zero. E. none of the above

5. Chapter 33 The Nature and Propagation of Light

6. 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 The nature of light

7. When light strikes a surface, it is (in general) both reflected and refracted. Reflection and refraction

8. Specular reflection occurs at a very smooth surface (left figure). • Diffuse reflection occurs at a rough surface (right figure). • Our primary concern is with specular reflection. Specular and diffuse reflection

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

10. Figure 33.8 below shows three important cases: • If nb > na, the refracted ray is bent toward the normal. • If nb < na, the refracted ray is bent away from the normal. • A ray oriented along the normal never bends. Reflection and refraction in three cases

11. The straight ruler in Figure 33.9(a) appears to bend at the surface of the water. • Figure 33.9(b) shows why. Why does the ruler appear to be bent?

12. Some indexes of refraction

13. Q33.2 Light passes from vacuum (index of refraction n = 1) into water (n = 1.333). If the incident angle qa is in the range 0° < qa < 90°, 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 qa .

14. A33.2 Light passes from vacuum (index of refraction n = 1) into water (n = 1.333). If the incident angle qa is in the range 0° < qa < 90°, 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 qa .

15. Q33.1 When light passes from vacuum (index of refraction n = 1) into water (n = 1.333), 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.

16. A33.1 When light passes from vacuum (index of refraction n = 1) into water (n = 1.333), 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.

17. Q33.3 Light passes from a medium of index of refraction na into a second medium of index of refraction nb. The angles of incidence and refraction are qa and qb, respectively. If na < nb, Aqa > qb and the light speeds up as it enters the second medium. B. qa > qb and the light slows down as it enters the second medium. C. qa < qb and the light speeds up as it enters the second medium. D. qa < qb and the light slows down as it enters the second medium.

18. A33.3 Light passes from a medium of index of refraction na into a second medium of index of refraction nb. The angles of incidence and refraction are qa and qb, respectively. If na < nb, Aqa > qb and the light speeds up as it enters the second medium. B. qa > qb and the light slows down as it enters the second medium. C. qa < qb and the light speeds up as it enters the second medium. D. qa < qb and the light slows down as it enters the second medium.

19. Light striking at the critical angle emerges tangent to the surface. (See Figure 33.13 below.) • If a > crit, the light is undergoes total internal reflection. Total internal reflection

20. A binocular using Porro prisms (below) and a “light pipe” (right) make use of total internal reflection in their design. Some applications of total internal reflection

21. Diamonds sparkle because they are cut so that total internal reflection occurs on their back surfaces. See Figure 33.17 below. A diamond and a periscope

22. Dispersion: The index of refraction depends on the wavelength of the light. See Figure 33.18 (right). • Figure 33.19 (below) shows dispersion by a prism. Dispersion