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Physics Lecture 8: Wave Nature of Light and Interference Experiments

This physics lecture covers the wave nature of light, including Huygen's wave theory and Newton's particle theory. It also discusses Maxwell's revolution in electromagnetism and Faraday's law. The lecture explores interference experiments like Young's double-slit and single-slit diffraction. Examples and qualitative explanations are provided.

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Physics Lecture 8: Wave Nature of Light and Interference Experiments

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  1. Physics 113 Lecture 8 Quiz 2 mean 12-13 Too Low, Will make easier Quizzes will be curved if average best-of-5 below 80 Last Time: Standing Waves pressure node = displacement antinode pressure antinode = displacement node L

  2. Wave Nature of Light Huygen’s (1579-1625) – Wave Newton (1642-1727) - Particle Maxwell’s Revolution (1864) Electromagnetism →transverse electromagnetic wave Faraday’s law Maxwell =3.0x108 m/s E=cB → Wave Nature Not obvious since  small Permittivity Permeability Changing E induces Change B induces Changing E induces Changing B … Oscillating Charge  Change E Field (Break-Off Electromagnetic Wave)

  3. Electromagnetic Spectrum No limit on  remember: f=c Red – 600 nm Violet – 400 nm 1 nm = 10-9 m Since light is a wave on get constructive and destructive interference

  4. Young’s Double Slit Experiment 1803 Just like speakers – send light through slits (view on distant screen) From diagram: constructive destructive where m=…-3,-2,-1,0,1,2,3,…

  5. View on a distant screen y  L For small  use (radians): Example (red light Young’s Experiment): light coherent (in phase) Find bright fringes L=15 m so use small angle approx. d=1mm=1x10-3 m =664 nm =664x10-9 m  plug in numbers: m=0 y=0.0 cm m=1 y=1.0 cm m=2 y=2.0 cm

  6. Diffraction Single Slit Just like sound light diffracts Dark Fringe (destructive interference): m=1,2,3,,,, Note: no m=0, the center is a light fringe

  7. Example (red light Single Slit): light coherent (in phase) measure distance on screen between central bright max to first minimum y=10cm L=15 m so use small angle approx. W=0.1mm=1x10-4 m =? so =y/L=0.1/15=0.00667 rads 10 cm • So this red light has wavelength 667 nm! • Using either single or double slit we can measure • wavelength of light

  8. Qualitative: Young’s Experiment (Double slit) as d decreases  increases -> larger fringe separation as  increases  increases -> larger fringe separation Qualitative: Single slit as W decreases  increases -> larger central fringe as  increases  increases -> larger central fringe

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