8B - 16_Interference_11.ppt

8B - 16_Interference_11.ppt - General Properties 0f Waves...

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General Properties 0f Waves If it is a wave, it usually has the following physical properties. What we learn about EM waves applies to sound waves and waves of elementary particles: Wavelength Frequency Energy Momentum Pressure Polarization Reflection Refraction Diffraction Interference Localization by superposition of various wavelengths Total Internal Reflection - Frustrated (Tunnel) Standing waves (modes of vibration)
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Huygens' Principle All points on a wavefront serve as point sources of secondary wavelets. After a time t , the new position of the wavefront will be that of a surface tangent to these secondary wavelets. Physically, the driven oscillators reemit waves of same frequency; speed of wave and wavelength may change.
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Phase of Wave A sine wave can be thought of as sweeping through 360º. Amplitude of wave is the x-projection of a rotating unit vector. The phase is the angle that has been swept. ! Phase difference between 2 waves = angular difference between 2 comparable points. 90º in this example.
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Phase differences give Interference Phase difference can be stated in A) Angle (degrees, radians = 2 π {path diff. / λ }) B) Fraction of a wavelength Superpose 2 waves Result: 0º, 0 rad. in phase 180º, π λ /2 120º, 2 π /3 λ /3
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Interference - the math Add two sinusoids of same frequency and amplitude, in same direction,but differing phases :
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Resultant Waves http://www.kettering.edu/~drussell/Demos/superpositi on/superposition.html
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Criteria for Interference Same frequency Phase difference - due to path, material, or reflection difference Stable phase (coherence) Use split light or laser Same polarization …. Then can add 2 or more waves
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Essence of waves: 1 + 1 = ? http://www.teachspin.com/instruments/two_slit/experiments.shtml Two one-slit patterns superpose to give a series of narrow peaks. The envelope of the two-slit pattern is the one-slit pattern.
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Phase Difference by Path - Michelson's Interferometer Michelson's interferometer, showing the path of light originating at point P of an extended source S. Mirror M splits the light into two beams, which reflect from mirrors M 1 and M 2 back to M and then to telescope T . In the telescope an observer sees a pattern of interference fringes. Michelson and Morley were not able to detect a change in speed of light due to motion of the Earth. This is explained by Special Relativity which says c = constant.
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Demo - Michelson Interferometer Microwave interference by multiple reflection - Michelson’s interferometer Changing the path length in one arm produces a series of maxima and minima at the detector.
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8B - 16_Interference_11.ppt - General Properties 0f Waves...

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