lecture8 (chap 8)

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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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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Experimental evidence that light consists

of photons comes from a phenomenon

called the pho toelectr ic effect.


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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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electronejecttoneededwork

MinimumenergyPhoton

electronejectedofenergykinetic

Maximum

maxKE oWhf

E=Wo, min work


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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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29.4The 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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Neutron diffraction is a manifestation of the wave-like properties

of particles.

f


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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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Part ic les are waves of probabi l i ty.

lecture8 (chap 8)

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