Polarization of Reflected LightP. J. Ouseph Citation: The Physics Teacher 40, 438 (2002); doi: 10.1119/1.1517889 View online: http://dx.doi.org/10.1119/1.1517889 View Table of Contents: http://scitation.aip.org/content/aapt/journal/tpt/40/7?ver=pdfcov Published by the American Association of Physics Teachers Articles you may be interested in Circular reflections Phys. Teach. 51, 121 (2013); 10.1119/1.4775542 Reflection of a polarized light cone Am. J. Phys. 81, 24 (2013); 10.1119/1.4765079 Polarization of light by reflection and the Brewster angle Am. J. Phys. 69, 1166 (2001); 10.1119/1.1397457 A quick experiment on reflection from concave mirrors Phys. Teach. 38, 206 (2000); 10.1119/1.880505 Puddle of light Phys. Teach. 37, 468 (1999); 10.1119/1.880365

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438 THE PHYSICS TEACHER � Vol. 40, October 2002

Apparatus

for Teaching PhysicsPolarization of Reflected Light

P.J. Ouseph, Physics Department, University of Louisville, Louisville, KY 40292; pjouseph@louisville.edu

Students in both calculus-basedand noncalculus-based courses

are introduced to the topic of polar-ization of reflected light.1 In thesecourses, variation of the level of po-larization with angle of incidenceand the Brewster angle are often dis-cussed. The apparatus discussed herecan demonstrate variation of polar-ization of reflected light as a functionof angle of incidence, including max-imum polarization at the Brewsterangle. The significance of the Brew-ster angle is that when unpolarizedlight falls on a smooth reflecting sur-face of a dielectric material with theangle of incidence equal to the Brew-ster angle, polarization of reflectedlight is perpendicular to the plane ofincidence. That is, in the reflectedlight the intensity of light with otherdirections of polarization will be the

lowest. If light falling on the surfaceis polarized, the level of polarizationand the intensity of the reflectedlight depend on the direction of po-larization with respect to the plane ofincidence. When the angle of inci-dence is equal to the Brewster angle,if the incident light is polarized per-pendicular to the plane of incidence,partial reflection occurs, and if lightfalling on the surface is polarized inthe plane of incidence, reflected lightintensity is extremely small.

The apparatus consists of a raybox, an acrylic prism, a glass slide,and a polarizing sheet. The compo-nents used are easily available fromscientific equipment suppliers.2 Theray box gives parallel rays of lightfrom one end and diverging raysfrom the other end. Figure 1 showsthe arrangement used to demonstrate

the polarization of the reflected lightat Brewster angle. In Fig. 1(a) theacrylic prism is placed so that theparallel rays fall symmetrically ontwo sides of the prism. The angle ofincidence of the rays falling on bothsides of the prism is 60�, which isvery close to the Brewster angle,57.5�, of acrylic. Notice that inFig. 1(a) the polarizer is oriented sothat only light polarized in a direc-tion perpendicular to the plane of in-cidence falls on the prism. In thiscase the reflected rays are clearly seen.In Fig. 1(b) the polarizer is rotated90� from its original position; there-fore, the polarizer allows only hori-zontally polarized light to fall on the

Erlend H. Graf, Column Editor Department of Physics & Astronomy, SUNY–Stony Brook, Stony Brook, NY 11794; egraf@notes.cc.sunysb.edu

Fig. 1. Parallel rays of light from a ray box fall on two sides of a prism. (a) Thepolarizer in front of the ray box is oriented so that only light polarized perpen-dicular to the plane of incidence falls on the prism. (b) Reflected rays are notseen when the polarizer orientation is changed from vertical to horizontal direction.

(a) (b)

Fig. 2. Polarizer is oriented in the hor-izontal direction. The angle of inci-dence for the fourth ray is equal to theBrewster angle, and therefore thefourth reflected ray is not seen.

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THE PHYSICS TEACHER � Vol. 40, October 2002 439

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srays except the fourth ray of light areseen in the figure because the angleof incidence for the fourth ray isequal to the Brewster angle. Theother rays with angles of incidenceless than and greater than the Brew-ster angle are visible because at otherangles horizontally polarized light isreflected by the acrylic surface.

This is the easiest and quickestway of demonstrating the differentaspects of polarization of reflectedlight.

References1. D. Halliday, R. Resnick, and J.

Walker, Fundamentals of Physics, 6th ed. (Wiley, New York, 2001),

pp. 824–825; D. Giancoli, Physics,5th ed. (Prentice Hall, EnglewoodCliffs, NJ, 1998), pp. 748–749.

2. The ray box shown in Figs. 1 and 2is from a 30-year-old ray optics kit.We could not find any informationabout the supplier of this kit. The 4-in-1 light source from PASCO (Cat-alog # OS-8517, 2002 Catalog, p.195; http://www.pasco.com) may beused for this experiment. The acrylicprism may be obtained from Sar-gent–Welch (Catalog # CP85506-05, 2001-2002 Catalog, p. 770;http:// www.sargentwelch.com). Po-larizer sheet is obtained from Ed-mund Industrial Optics (Catalog #L38-491, 2001 Catalog, p. 80;http://www.edmundoptics.com).

prism. As expected, the reflected raysare not seen [Fig. 1(b)].

Angular dependence of polariza-tion of reflected light can be demon-strated with the help of the divergingrays. A glass reflector is placed sothat the angle of incidence of the raysfalling on the glass is lower than,equal to, and higher than the Brew-ster angle of glass. The glass reflectoris a microscope slide held by an alu-minum holder. The inside of thealuminum holder is painted black toreduce reflection. In Fig. 2 the polar-izer is held in an orientation allowingonly the horizontally polarized lightto pass through. All the reflected

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1. Richard Hassler, Trimble Navigation Ltd., 7403 Church Ranch Blvd. Suite 100, Westminster, CO

80021.

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