Physics 213 General PhysicsExam 2PowerPoint PresentationInterference PatternsDiffractionDiffraction PatternSingle Slit DiffractionSingle Slit Diffraction, 2Single Slit Diffraction, 3Single Slit Diffraction, 4Slide 11Slide 12Diffraction GratingDiffraction Grating, finalPolarization of Light WavesPolarization of Light, contSlide 17Polarization by Selective AbsorptionPolarization by Scattering, contPhysics 213General PhysicsLecture 18Exam 2+12 additional points will be added to each score.3Last Meeting: InterferenceToday: Diffraction and PolarizationInterference PatternsConstructive interference occurs when waves arrive in phaseDiffractionHuygen’s principle requires that the waves spread out after they pass through slitsThis spreading out of light from its initial line of travel is called diffractionIn general, diffraction occurs when waves pass through small openings, around obstacles or by sharp edgesDiffraction PatternA single slit placed between a distant light source and a screen produces a diffraction patternIt will have a broad, intense central bandThe central band will be flanked by a series of narrower, less intense secondary bandsCalled secondary maximaThe central band will also be flanked by a series of dark bandsCalled minimaSingle Slit DiffractionAccording to Huygen’s principle, each portion of the slit acts as a source of wavesThe light from one portion of the slit can interfere with light from another portionThe resultant intensity on the screen depends on the direction θSingle Slit Diffraction, 2All the waves that originate at the slit are in phaseWave 1 travels farther than wave 3 by an amount equal to the path difference (a/2) sin θ If this path difference is exactly half of a wavelength, the two waves cancel each other and destructive interference resultsSingle Slit Diffraction, 3In general, destructive interference occurs for a single slit of width a when sin θdark = mλ / am = 1, 2, 3, …Doesn’t give any information about the variations in intensity along the screenSingle Slit Diffraction, 4The general features of the intensity distribution are shownA broad central bright fringe is flanked by much weaker bright fringes alternating with dark fringesThe points of constructive interference lie approximately halfway between the dark fringes11sin θdark = mλ / a m = 1, 2, 3, …sin θbright = mλ / d m =0 1, 2, 3, …There are two difficulties in using a double slit for measuring wavelengths. 1. The bright linesbright lines on the screen are actually extremely faintfaint and an intense light source is therefore required;2. The lines are relatively broad and it is hard to locate their center accurately.Diffraction GratingThe condition for maxima isd sin θbright = m λm = 0, 1, 2, …The integer m is the order number of the diffraction patternIf the incident radiation contains several wavelengths, each wavelength deviates through a specific angleDiffraction Grating, finalAll the wavelengths are focused at m = 0This is called the zeroth order maximumThe first order maximum corresponds to m = 1Note the sharpness of the principle maxima and the broad range of the dark areaThis is in contrast to the broad, bright fringes characteristic of the two-slit interference patternPolarization of Light WavesEach atom produces a wave with its own orientation of All directions of the electric field vector are equally possible and lie in a plane perpendicular to the direction of propagationThis is an unpolarized waveEPolarization of Light, contA wave is said to be linearly polarized if the resultant electric field vibrates in the same direction at all times at a particular pointPolarization can be obtained from an unpolarized beam by Selective absorptionReflectionScatteringExamples of Polarized LightPolarization by Selective AbsorptionThe most common technique for polarizing lightUses a material that transmits waves whose electric field vectors in the plane are parallel to a certain direction and absorbs waves whose electric field vectors are perpendicular to that directionE=E0cosI=I0cos2Polarization by Scattering, contThe horizontal part of the electric field vector in the incident wave causes the charges to vibrate horizontallyThe vertical part of the vector simultaneously causes them to vibrate verticallyHorizontally and vertically polarized waves are
View Full Document
Unlocking...