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

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”)

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

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

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

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

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.

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

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

Lecture ©2008 by W.H. Freeman and Company

Lecture n 1 sin θ 1 = n 2 sin θ 2 Snell’s Law of Refraction

Lecture 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.

Lecture ©2008 by W.H. Freeman and Company

Lecture ©2008 by W.H. Freeman and Company

Lecture ©2008 by W.H. Freeman and Company

Lecture 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.

Lecture LIGHT PIPES 7A-24

Lecture ©2008 by W.H. Freeman and Company

Lecture DEMO PRISM AND COLORS 7A-22

Lecture ©2008 by W.H. Freeman and Company

Lecture 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

Lecture 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

Lecture 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.

Lecture PHYSICS 241 November 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

Lecture PHYSICS 241 November 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 = 30 O. What is the index of refraction of the glass? A| 1.33 B| 1.41 C| 1.65 D| 2.10

Lecture PHYSICS 241 April 7, :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

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

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