lecture8 (chap 8)
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7/28/2019 Lecture8 (Chap 8)
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Particle Waves and Atomic Physics
The wave duality
Photons and the photoelectric effect
The momentum of a photon and the Compton
effect
The De Broglie wavelength and the wave nature
of matter
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7/28/2019 Lecture8 (Chap 8)
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29.1Wave Part icle Duali ty
When a beam of electrons is used in a
Youngs double slit experiment, a fringepattern occurs, indicating interference
effects.
Waves can exh ibi t part ic le-l ike character is t ics,
and p art ic les c an exhibi t wave-l ike character is t ics.
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29.3Photons and the Photoelectr ic Effect
Electromagnetic waves are composed of particle-like
entities called photons .
hfE hp
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29.3Photons and the Photoelectr ic Effect
Experimental evidence that light consists
of photons comes from a phenomenon
called the pho toelectr ic effect.
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29.3Photons and the Photoelectr ic Effect
When light shines on a metal, a photon can give up its energy to an electron
in that metal. The minimum energy required to remove the least strongly
held electrons is called the work funct ion .
electronejecttoneededwork
Minimum
electronejectedofenergykinetic
Maximum
max
energyPhoton
KE oWhf
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29.3Photons and the Photoelectr ic Effect
electronejecttoneededwork
MinimumenergyPhoton
electronejectedofenergykinetic
Maximum
maxKE oWhf
E=Wo, min work
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29.3Photons and the Photoelectr ic Effect
Examp le 2The Photoelectric Effect for a Silver Surface
The work function for a silver surface is 4.73 eV. Find the minimumfrequency that light must have to eject electrons from the surface.
oo Whf
J0
maxKE
Hz1014.1sJ106.626 eVJ1060.1eV73.415
34
19
hWf oo
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29.3Photons and the Photoelectr ic Effect
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29.3Photons and the Photoelectr ic Effect
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29.4The Momentum of a Photon and the Compto n Effect
The scattered photon and
the recoil electron depart the
collision in different directions.
Due to conservation of energy,
the scattered photon must have
a smaller frequency.
This is called the Comp ton effect .
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29.4The Momentum of a Photon and the Compto n Effect
Momentum and energy areconserved in the collision.
cos1
mc
h
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29.5The de Brog l ie Wavelength and the Wave Nature of Matter
The wavelength of a particle is givenby the same relation that applies to a
photon:
ph
de Brog l ie wavelength
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29.5The de Brog l ie Wavelength and the Wave Nature of Matter
Neutron diffraction is a manifestation of the wave-like properties
of particles.
f
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29.5The de Brog l ie Wavelength and the Wave Nature of Matter
Example 5The de Broglie Wavelength of an Electron and a Baseball
Determine the de Broglie wavelength of (a) an electron moving at a speedof 6.0x106 m/s and (b) a baseball (mass = 0.15 kg) moving at a speed
of 13 m/s.
m102.1sm100.6kg101.9
sJ1063.6 10631
34
ph
m103.3
sm13kg15.0sJ1063.6 34
34
ph
29 5 Th d B li W l th d th W N t f M tt
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29.5The de Brog l ie Wavelength and the Wave Nature of Matter
Part ic les are waves of probabi l i ty.
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