Physics 52 - Heat and Optics Dr. Joseph F. Becker Physics Department San Jose State University © 2005 J. F. Becker

Chapter 33 The Nature and Propagation of Light © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Spherical E-M wave fronts spreading out uniformly in all directions from a point source of LIGHT © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Spherical wave fronts. When wave fronts are planes the rays are parallel. © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics Wave fronts and rays.

A plane wave is in part reflected and in part refracted at the boundary between two media (air and glass here). © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics air glass

Specular and diffuse reflection © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Reflection and refraction for the case where n b > n a glass air © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Optical materials are characterized by an important property called the index of refraction or refractive index defined as: n = c / v n where c is the speed of light in vacuum and equal to c = 3.00 (10) 8 m/s, and v n is the speed of light in the material. The value of v n varies from one material to another (type of molecules, crystal structure, etc.). n is always equal to, or greater than, 1.00 © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

A twice reflected ray (done in the lab) © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

As light passes through the interface between two materials (like air and glass) the frequency (f) of the light wave remains the same: number of cycles per second out of one material must equal the number of cycles/second into the other. IN VACUUM: f = c /  IN MATERIAL: f = v n / n Equating the f’s the we get c /  = v n / n n =  (v n / c) so n =  / (n) © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Law of REFLECTION Angle of incidence = angle of reflection  i =  r Law of REFRACTION (Snell’s Law) © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics n 1 sin  1 = n 2 sin  2

A light ray is incident on a block of glass (n = 1.50) making an angle of 30 o with the NORMAL to the surface. a) What is the angle of reflection? b) What is the angle of refraction? © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Total internal reflection (FIBER OPTICS)

Light trapped in a fiber optic glass communications cable: total internal reflection © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Variation of index of refraction (n) with wavelength of light in vacuum (  ). The wavelength of light in the material is n     n 700 © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Dispersion of light by a prism. The band of colors is called a spectrum. © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Rainbows are formed by refraction, reflection, and dispersion in water drops: (a) Primary rainbow (b) Secondary rainbow red violet © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

The rainbow mechanism again © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Polarization (a) Transverse wave on a string, polarized in the y-direction. (b) Wave polarized in the z-direction. (c) Barrier with vertical slot passes the y- and blocks the z-polarized components. © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Polaroid filter © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Unpolarized light is incident on a polarizing filter Law of Malus: I(  ) = I max cos 2  © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Reflected light can be polarized © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

  P is the polarizing angle (Brewster’s angle) © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Light striking the water-air interface (a) from the air side (b) from the water side © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Blue sky and red sunset. Scattered light contains mostly blue light (sky) and the white sunlight that has lost some blue appears red (sunset). © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Huygens’ Principle Every point on a wave front may be considered a source of secondary wavelets. © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Reflection © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Refraction © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Dispersion © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Lateral beam displacement (Lab) © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics

Review © 2005 J. F. Becker San Jose State University Physics 52 Heat and Optics