Lidia Nicolai and Maximo Barim Departamento de ~ k i c aFacultad , de Ciencias Exactas y Naturales. Pabellbn l-C. The concept of polarized waves appears somewhat difficult to understand and visualize hy our natural science students. To overcome this prohlem a simple device was built to show how any type of polarized wave (plane, circular, and elliptical) can he obtained from two coherent planar waves having their vibration planes perpendicular to each other. The device was huilt using 2-mm-thick colorless, acrylic sheet (Fig. 1). It contains essentially two plates: one fixed vertically (x, y plane) and one movable horizontally (x, z plane). Each plate has a wave drawn of exactly the same wavelength and amplitude. They represent, for a fixed t value: E, = EOysin ( k z - wt) E, = E, sin (kx - w t
+ 9)
in both cases values of E are marked for nl/zrX (n = 1,2,3,
Universitaria. 1428 Buenos Aires. Argentina
. . .). 9 can he any phase difference: 9 = 0 or 9 # 0.
The horizontal plate (containing E,) can he made to slide so that its nodes coincide with any position of E, creating a phase difference of 9 = "1% (n = 1, 2,3, . ..). When the device is looked a t facing the x axis (propagation) (Figs. 2 and 3), the wave front can heviewed as a square (Figs. 2h and 3h) because Eo, = Ek. The influence of the phase difference 9 can he described as shown in the table. Furthermore, the device can also he built with two waves of different maximum amplitudes (Eo, # Eo,) but with equal values of wavelength (A). In this case moving one plate would lead to linear or elliptical polarization only. The device is simple to build and operate and has proved exceptionally useful to help visualize the formation of polarized light. The students can handle it without difficulties, create their own problems and questions, and discuss them with the teaching staff.
Iniluence of the Phase Difference (D Type 01 Polarir.
n Ooreven muiiiple0f~7,~0 or 2 r Odd munlple 01 'Y, r 6 "k 3 %S any other any other
linear linear circular circular elliptical
Direction of rotation
Quadrant
-
1 and 3 2 and 4
-
dextroroiatory levorotatory depending on 9
Figwe 1. A side view of the device.
a
Figure 2. PlanepolarizedIlgM. (a)The plane of vibration fw 9 = 0. (b) They, z components of the electric vector at a fixed point x.
b
Figure 3. RlgM ciroular-polarized Ilght. (a)The Evectors along the xaxis tor 9 = r12. (b) Rotation 01 electric vector at a fixed point x.
Volume 67 Number 8 August 1990
847
