wave? particles??
DESCRIPTION
Wave? Particles??. Physics 100 Chapt 22. Maxwell. E. B. Light is a wave of oscillating E- and B-fields. James Clerk Maxwell. Einstein. Light is comprised of particle-like quanta called photons. h l. p = . E=hf . Who’s right??. Waves explain diffraction & interference - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/1.jpg)
Wave? Particles??
Physics 100Chapt 22
![Page 2: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/2.jpg)
Maxwell
Light is a wave of oscillating E- and B-fields
James Clerk Maxwell
E
B
![Page 3: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/3.jpg)
Einstein
Light is comprised of particle-like quantacalled photons
E=hf
hp =
![Page 4: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/4.jpg)
Who’s right??
Waves explain diffraction & interference
Photons explain photoelectric effect & Compton scattering
![Page 5: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/5.jpg)
Impossible to explain interference with particles
With 2 slits openno light goes here
Block off one slitNow light
can go here
![Page 6: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/6.jpg)
Impossible to explain PE-effectand Compton scattering with waves
Electron KE (electron Volts)
red
0.5 1.0 1.5
yellow
blueviolet
![Page 7: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/7.jpg)
Make an intereferencepattern with low intensity light
One photon at a time goes through the two-slit apparatus
The interference pattern emerges one dot at a time
![Page 8: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/8.jpg)
Wave-Particle “duality
-Light behaves like a wave when it propagates through space-And as a particle when it interacts with matter
![Page 9: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/9.jpg)
Photon photography
![Page 10: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/10.jpg)
Louis de Broglie
If light behaves as particles, maybe other particles (such as electrons) behave as waves h
p = Photons:
hp =
particles:
hp =
Wave-particle duality is
a universal phenomenon
![Page 11: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/11.jpg)
Ordinary-sized objects have tiny wavelengths
0.2kg30m/s
hp = h
mv= 6.6x10-34Js0.2kg x 30 m/s =
6.6x10-34Js6.0 kg m/s = 1.1x10-34m =
Incredibly small
![Page 12: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/12.jpg)
the wavelength of an electronis not so small
9x10-31 kg 6x106 m/s
hp = h
mv= 6.6x10-34Js9x10-31kg x 6x106 m/s =
6.6x10-34Js5.4x10-24 kg m/s = 1.2x10-10m =
-
About the size of an atom
![Page 13: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/13.jpg)
Send low-momentum electrons thru narrow slits
See a diffraction pattern characteristic of
wavelength =h/p as predicted by de Broglie
![Page 14: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/14.jpg)
Light thru a small hole
“Diffraction”rings
![Page 15: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/15.jpg)
Matter waves(electrons through a crystal)
“Diffraction”rings
![Page 16: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/16.jpg)
Waves thru a narrow slit
py
py
y
x
y
![Page 17: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/17.jpg)
Waves thru a narrower slit
wider
py
py
y
When the slit becomes narrower, thespread in vertical momentum increases
x
y
![Page 18: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/18.jpg)
Heisenberg Uncertainty Principle
y py > hUncertaintyin location
Uncertainty in
momentum in
that direction
If you make one of these smaller, the other has to become bigger
![Page 19: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/19.jpg)
Heisenberg tries to measure the location of an atom
For better precision, usea shorter wavelength
But then the momentumchange is higher
x px > h
![Page 20: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/20.jpg)
Localize a baseball
0.2kg x px > h px > hx
Suppose x= 1x10-10m
px > 6.6x10-34Js1x10-10m
vx >
= 6.6x10-24kgm/s
A very tiny uncertainty
About the size of a single atom
px m
6.6x10-44Js0.2kg = = 3.3x10-23 m/s
![Page 21: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/21.jpg)
Localize an electron
x px > h px > hx
Suppose x= 1x10-10m
px > 6.6x10-34Js1x10-10m
vx >
= 6.6x10-24kgm/s
Huge, about 2% of c
About the size of a single atom
px me
6.6x10-24Js9x10-31kg = = 7x106 m/s
-me=9x10-31kg
![Page 22: Wave? Particles??](https://reader035.vdocuments.mx/reader035/viewer/2022062218/56815fb0550346895dceab4a/html5/thumbnails/22.jpg)
uncertainty is inherentin the quantum world