9 - the compton effect

7/25/2019 9 - The Compton Effect

1/26

Lesson 9Lesson 9


2/26

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


3/26


4/26


5/26


6/26


7/26


8/26


9/26


10/26


11/26


12/26


13/26

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$


14/26


15/26

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+


16/26

Expected vs. Actual ResultsExpected vs. Actual Results

ExpectedExpected

ActualActual


17/26

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$


18/26


19/26

Interpretation

e used Einsteins equation Emc2to

produce an expression for this

momentum of an E'( particle

)photon*$

pE4c h4


20/26

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


21/26

"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$


22/26

$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 ;


23/26


24/26


25/26


26/26

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$66 x 161>?$

9 - the compton effect

Documents