1. Lecture 22-1 Maxwell’s Rainbow Light is an Electromagnetic Wave

2. Lecture 22-2 The Speed of Light Classic experiments to measure the speed of light:  Galileo (lantern and shutter)  Römer (eclipses of Io behind Jupiter)  Fizeau (toothed wheel)  Foucault (plane rotating mirror)  Michelson (octagonal rotating mirror)  Michelson and Morley (interferometer) Speed of light is not infinite! Speed of light is not dependent on the motion of source/observer (no fixed “ether”)

3. Lecture 22-3 ©2008 by W.H. Freeman and Company

4. Lecture 22-4 Refraction and Transmission incident ray reflected ray refracted ray Medium 1 Medium 2 When light encounters an interface between different media, it can generally both reflect and refract. (This speed can even depend on wavelength.) Light can travel through matter medium as well as free space (vacuum). Inside matter, the speed of light v is generally less than c. index of refraction

5. Lecture 22-5 Determine the speed of light c using static measurements __1____ = 2.99792458 m/s √ ( ε o μ o ) ε o = 8.8541 x 10 -12 C 2 /(N.m 2 ) μ o = 4π x 10 -7 N/A 2 Coulomb’s law Ampere’s law

6. Lecture 22-6 ©2008 by W.H. Freeman and Company

7. Lecture 22-7 PHYSICS 241 READING QUIZ 1 Which of the following statements is incorrect? A| The index of refraction depends on the color of the light. B| When a light ray travels in a medium with an index of refraction (n > 1) the wavelength of the light is shorter than the wavelength of the light in vacuum. C) When a light ray travels from air to a more dense medium ( n > 1) the refracted ray is bent away from the normal. D| Total internal reflection only occurs inside a medium with an index of refraction with n > 1.

8. Lecture 22-8 Huygens’s Principle Each point on a primary wavefront serves as the source of spherical secondary wavelets that advance with a speed and frequency equal to those of the primary wave. The primary wavefront at some later time is the envelope of these wavelets. t1t1 t2t2 t3t3 t1t1 t2t2 t3t3 points of given phase wavelet

9. Lecture 22-9 ©2008 by W.H. Freeman and Company

10. Lecture 22-10 ©2008 by W.H. Freeman and Company

11. Lecture 22-11 n 1 sin θ 1 = n 2 sin θ 2 Snell’s Law of Refraction

12. Lecture 22-12 Physics 241 WARMUP Quiz 2 Which of the following statements is incorrect? A| A transverse electromagnetic wave (TEM) has energy and momentum. B| The velocity of light is slower in translucent materials with a dielectric constant K>1. C| The electric vectors in a (TEM) wave define the polarization geometry of the light. D| Dipole electromagnetic radiation has perfectly spherical radiation pattern.

13. Lecture 22-13 ©2008 by W.H. Freeman and Company

14. Lecture 22-14 ©2008 by W.H. Freeman and Company

15. Lecture 22-15 ©2008 by W.H. Freeman and Company

16. Lecture 22-16 Laser Light amplification by stimulated emission of radiation Coherent, narrow, and intense Monochromatic (can be tunable as in liquid dye lasers) Can be continuous or pulsed Can be made using solid, liquid, gas, or even free electrons. Sustained population inversion is required.

17. Lecture 22-17 LIGHT PIPES 7A-24

18. Lecture 22-18 ©2008 by W.H. Freeman and Company

19. Lecture 22-19 DEMO PRISM AND COLORS 7A-22

20. Lecture 22-20 ©2008 by W.H. Freeman and Company

21. Lecture 22-21 Summary: Laws of Reflection and Refraction Law of Reflection A reflected ray lies in the plane of incidence The angle of reflection is equal to the angle of incidence Law of refraction A refracted ray lies in the plane of incidence The angle of refraction is related to the angle of incidence by Snell’s Law Medium 1 Medium 2 Where λ is the wavelength in vacuum

22. Lecture 22-22 Wave-Particle Duality of Light  Refraction, diffraction (Huygens’s Principle)  Interference (Young’s double slit interference)  Electromagnetic waves (Maxwell’s Equations)  Doesn’t require a medium  Light and other EM radiation often come together (e.g., in Black-body radiation)  Collisions, scattering as in photoelectric effect (Albert Einstein)  Energy is quantized: Planck’s constant  massless photons Quantum Mechanics: Duality for all particles Wave nature of light Particle nature of light

23. Lecture 22-23 Light Spectra Continuous spectrum (such as in sunlight or other thermal radiation) Line spectra H He Ba Hg  Single atoms (or dilute gases) emit or absorb light at discrete set of frequencies.

24. Lecture 22-24 PHYSICS 241 November 10, 2011 10:30 QUIZ 3 A light ray is incident on a plane glass surface with incident angle θ 1 = 45 O and the refracted ray has an angle θ 2 = 20 O. What is the index of refraction of the glass? A| 1.33 B| 2.65 C| 2.08 D| 1.20

25. Lecture 22-25 PHYSICS 241 November 10, 2011 11:30 QUIZ 3 A light ray is incident on a plane glass surface with incident angle θ 1 = 45 O and the refracted ray has an angle θ 2 = 30 O. What is the index of refraction of the glass? A| 1.33 B| 1.41 C| 1.65 D| 2.10

26. Lecture 22-26 PHYSICS 241 April 7, 2011 11:30 QUIZ 3 A light ray is incident on a plane glass surface with incident angle θ 1 = 30 O and the refracted ray has an angle θ 2 = 16 O. What is the index of refraction of the glass? A| 1.33 B| 1.41 C| 1.65 D| 1.80

27. Lecture 22-27 ©2008 by W.H. Freeman and Company Polarization by reflection

28. Lecture 22-28 ©2008 by W.H. Freeman and Company I = I O (cos θ) 2