University:
California State University, Northridge
Course:
PHYS 100B | General Physics II
Academic year:

2008
Views:

398

Pages:

11
Author:

Adelyn Pacheco

Chapter 25 Electromagnetic Waves Outline 25-1 The production of Electromagnetic Waves 25-3 The Electromagnetic Spectrum 25-4 Energy gy and momentum in Electromagnetic g Waves 25-5 Polarization 25-5 Polarization Natural N t l white hit lilight ht iis non-polarized, l i d since i th the itits E vector t off th the electromagnetic wave vibrates randomly in any direction. If the E vector vibrates only in one direction, the wave is said to be polarized --- linearly polarized. The electric field defines the polarization direction. Figure 25-11 25 11 Polarization of Electromagnetic Waves Representation of Polarization Figure 25-12 Fi 25 12 Polarized Versus Unpolarized Light Light Passing through Polarizer The polarizer is made of special material, and it allows light go through along one direction – called transmission axis. Figure 25-13 A Mechanical Analog of a Polarizer The Law of Malus (Transmission of Polarized Light Through a Polarizer) I = I 0 cos 2 θ (25 − 13) Where θ is the angle of the polarization direction of the linear polarized input light and the polarizer transmission axis Figure 25-14 Transmission of Polarized Li ht Through Light Th h a Polarizer P l i Exercise 25-5 Vertically polarized light with an intensity of 515 W/m2 passes through a polarizer oriented at an angle θ to the vertical (transmission axis of a polarizer). Find the transmitted intensity of the light for (a) θ=10.0º and (b) θ=45.0º, 4 0º and d (c) ( ) θ=90.0º. 90 0º Solution ( ) (a) I = I 0 cos 2 θ = (515W / m 2 ) cos 2 10.0° = 499 W / m 2 (b) I = I 0 cos 2 θ = (515W / m 2 ) cos 2 45.0° = 258 W / m 2 (c) I = I 0 cos 2 θ = (515W / m 2 ) cos 2 90.0° = 0 W / m 2 Transmission of an un-polarized light Figure 25-15 Transmission of Unpolarized Light Through a Polarizer Transmission of an un-polarized light 1 I = I0 2 It is independent to the angle θ. (25 − 14) A common experiment Figure 25-16 A Polarizer and an Analyzer Example 25-5 In the polarization shown in the sketch sketch, the final intensity of the beam is 0.200 I0. What is the angle θ between the transmission of the analyzer and polarizer? Example 25-5 Analyze This Active Exercise Calculate C l l t th the ttransmitted itt d iintensity t it ffor th the ffollowing ll i cases: [( [(a)) A vertically polarized beam of intensity I0 passes through a polarizer with its transmission axis at 60º to the vertical (transmission axis )]. (b) a vertical ti l polarized l i db beam off iintensity t it I0 passes through th h ttwo polarizers, the first with its transmission axis at 30º to the vertical, and the second with its transmission axis at 60º to the vertical.