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9 - The Compton Effect
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Transcript of 9 - The Compton Effect
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Lesson 9Lesson 9
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Objective
Explain, qualitatively and quantitatively,
how the Compton effect is an example
of wave particle duality, applying the
laws of mechanics and conservation of
momentum and energy to photons
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The Experiment
In 1923 Compton sent a eam of !"rays
with a #nown frequency at a loc# of
graphite$ %hen they hit the graphite, he
noticed that the frequency of the
reounding x"ray was lower than the
incident x"ray and an electron was
emitted$
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The Experiment
&he results could not e explained
using E'( wave theory$ In classical
E'( theory, if light was a wave without
mass, the light should pass through
the graphite with a smaller wavelength
)squished li#e ouncing a all* or
greaterfrequency+
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Expected vs. Actual ResultsExpected vs. Actual Results
ExpectedExpected
ActualActual
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Interpretation
ccording to -lanc#, energy is carriedin the frequency of E'($ lowerfrequency meant that energy was lost$
&he direction of the e.ected electronand deflected E'( indicated acollision$
fundamental principle of physics isthe conservation of momentum in /0collision$
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Interpretation
e used Einsteins equation Emc2to
produce an expression for this
momentum of an E'( particle
)photon*$
pE4c h4
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Equation or !ompton Eect
Compton derived an equation that considered x"raysas a particle$ 5sing Einsteins relativity theory,
conservation of momentum, conservation of energy,
and some complicated algera he came up with
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"ummar#
In the photoelectric and in the Comptonexperiment the results were interpreted aseing consistent with particle ehavior$
In fact, his calculations proved an almost1667 conservation of momentum$ &heparticle model of light )photons* '58& ecorrect
&his was a turning point in the particle theoryof light, when the ma.ority of physicistsstarted to elieve that the wave"particleduality of light was proaly correct$
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$ariables
%here: is the change in the wavelength of the
incident E'($ )%& f*
h4mec is #nown as the Compton wavelengthof the electron$
Cos' is the scattering angle of the E'($ Example x"rays of 2$66 x 16"16m are
scattered y some material$ &he scatteredE'( is detected at ;
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Examples
1$ Calculate the energy and momentum
of lue light with a wavelength of ;66
nm$
2$ Calculate the momentum of an x"ray
having a frequency of 3$66 x 161>?$