2The Wave Nature of Light 24.1 Waves Versus Particles
324.1 Waves Versus Particles Huygen’s principle – every point on a wave front can be considered as a source of tiny wavelets that spread out in the forward direction at the speed of the wave itself.24.1
424.1 Waves Versus Particles Particularly useful for analyzing when a wave hits an obstacleFor example reflection and refractionOr diffraction – the bendingof waves behindobstaclesDiffraction24.1
524.1 Waves Versus Particles Ray model of light can not account for diffraction24.1
724.3 Young’s Double-Slit Experiment Thomas Young (1801)Double Slit ExperimentLight from a singlesource (sun)Sent through athin slit first (soone point sourceof light3. Allowed to pass through two small slits24.3
824.3 Young’s Double-Slit Experiment If light is a ray we would expect two slits of lightThe actual pattern looked like thisCaused by constructive anddestructive interference24.3
924.3 Young’s Double-Slit Experiment The geometry of thepath of two rays oflightConstructive interference occurs when the path difference, equals a whole number of wavelengthsOr24.3
1024.3 Young’s Double-Slit Experiment For destructive interference the difference in distance has to be by some half wavelengthSom is called the orderConstructive interference – bright fringeDestructive interference – dark fringe24.3
1124.3 Young’s Double-Slit Experiment The distance between slits will depend on how far the screen is from the slits24.3
12S-106A monochromatic light with a frequency of 5.35x1014 Hz is shot through a set of double slits that are m apart and the resulting interference pattern is placed on a screen 1.5 m away. What will be the angle of the 3rd order maxima?
13S-107A monochromatic light with a frequency of 5.35x1014 Hz is shot through a set of double slits that are m apart and the resulting interference pattern is placed on a screen 1.5 m away. What is the minimum path difference between two waves that will allow a dark fringe to be produced?
1424.3 Young’s Double-Slit Experiment Brightness fades as distance increases from the 0th order maxima (central maxima)Applet24.3
1524.3 Young’s Double-Slit Experiment If white light is incident on slits, the central maxima is white, but rainbows occur at higher order maximaBecause different colors have different wavelengths24.3
16The Wave Nature of Light 24.4 The Visible Spectrum and Dispersion
1724.4 The Visible Spectrum and Dispersion Ranges from 750 nm (red) to 400 nm (violet)Dispersion - the spreading of white light into a spectrum24.4
1824.4 The Visible Spectrum and Dispersion PrismThe index of refraction for each frequency is slightly different, so the angle of refraction differs24.4
1924.4 The Visible Spectrum and Dispersion RainbowCaused by refractionand internalreflection24.4
20The Wave Nature of Light 24.5 Diffraction by a Single Slit of Disk
2124.5 Diffraction by a Single Slit of Disk If light is a wave, then light from a point source will diffract around a disk and create a constructive interference point in the middle of the shadowA single slit will produce a pattern for the same reasonApplet24.5
22The Wave Nature of Light 24.6 Diffraction Grating
23Diffraction Grating – a large number of equally spaced parallel slits The maxima are sharperand brighter for adiffraction gratingEquations are the same24.6
24S-109A rabid raccoon shoots a laser through a diffraction grating. The frequency of the light is 4.11x1014 Hz. The result is a interference pattern on a wall 2.5 m from the diffraction grating. If the 1st order minima is located 12.4 cm above the center, how many slits per cm are on the diffraction grating?
25The Wave Nature of Light 24.8 Interference by Thin Films
2624.8 Interference by Thin Films Occur when films are just a few wavelengths thickSoap BubblesOil24.8
2724.8 Interference by Thin Films Light strikes a surfaceSome of the lightreflectsrefracts, thenreflects off the other boundaryIf the path difference ABC = nl, then constructive interferenceIf the path difference ABC = (n+½)l, the destructive interference24.8
2824.8 Interference by Thin Films The wavelength of light in a medium is given as24.8
30Light is Polarized when it only vibrates in one plane 24.10 PolarizationLight is Polarized when it only vibrates in one planeDemo24.10
31S-110Light with a wavelength of 482 nm is incident on a thin layer of oil (n=1.45). The light strikes at an angle of 38o from the normal. What is the minimum thickness of oil that would cause an interference pattern to form?
32S-112Light strikes a block of plastic (n=1.4) at an angle of 28o to the normal. Using the diagram below calculate the angle that it will exit the block.random walrusq=42o