1. pressure node = displacement antinode
Physics 113
Lecture 8
Quiz 2 mean Too Low, Will make easier
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Standing Waves
pressure node = displacement antinode
pressure antinode = displacement node L

2. Wave Nature of Light Huygen’s (1579-1625) – Wave
Newton ( ) - 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 screeny  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= y=0.0 cm
m= y=1.0 cm
m= 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= 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