![]() ![]() ![]() A large number of parallel, closely spaced slits constitutes a diffraction grating.A diffraction grating uses diffraction and interference to disperse light into its component colors.Section2 Diffraction: Diffraction Gratings Light diffracted by an obstacle also produces a pattern.In a diffraction pattern, the central maximum is twice as wide as the secondary maxima.Section2 Diffraction: The Bending of Light Waves Wavelets (as in Huygens’ principle) in a wave front interfere with each other. ![]() Light waves form a diffraction patternby passing around an obstacle or bending through a slit and interfering with each other.Diffraction isa change in the direction of a wave when the wave encounters an obstacle, an opening, or an edge.Section2 Diffraction The Bending of Light Waves Given:d = 3.0 10–5 m m = 2 q= 2.15º Unknown: l= ? Equation: d sin q = ml The second-orderbright fringe (m = 2) is measured on a viewing screen at an angle of 2.15º from the central maximum. Section1 Interference: Demonstrating Interference Chapter 15 Sample Problem The distance between the two slits is 0.030 mm. Equation for destructive interference d sin q = ±(m + 1/2)l m = 0, 1, 2, 3, … The path difference between two waves = an odd number of half wavelength.Equation for constructive interference d sin q = ±ml m = 0, 1, 2, 3, … The path difference between two waves = an integer multiple of the wavelength.The first maximum on either side of the central maximum (m = 1) is called the first-order maximum.The central bright fringe at q = 0 (m = 0) is called the zeroth-order maximum, or the central maximum.The order number is represented by the symbol m. The number assigned to interference fringes with respect to the central bright fringe is called the order number. Constructive interference occurs when dsinqequals l, 2l, 3l, … or ml where m= 0, 1, 2, 3, ….The path difference is the difference in the distance traveled by two beams when they are scattered in the same direction from different points.Bright fringes result from constructive interference and dark fringes result from complete destructive interference. The location of interference fringes can be predicted.Section1 Interference: Demonstrating Interference Conditions for Interference of Light Waves If monochromatic light is used, the light from the two slits produces a series of bright and dark parallel bands, or fringes, on a viewing screen.Interference can be demonstrated by passing light through two narrow parallel slits.Section1 Interference: Demonstrating Interference ![]() Source Source monochromatic and coherent monochromatic Superposition of Waves Which two waves are in phase and which two waves are out of phase? In Phase Out of Phase
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