pressure node = displacement antinode 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
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)
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
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,…
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
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
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
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