INTERFERENCE(&(DIFFRACTION(OF(WAVES(+(3(BASIC(TENETS(OF(QUANTUM(MECHANICS(
• What%does%interference%mean?%(Sec3ons%17.1%&%17.5)%
: Construc3ve%and%Destruc3ve%interference%
: Both%Transverse%and%Longitudinal%Waves%interfere%
%%
• Standing%Waves%&%the%1st$basic$tenet$of$QM:%Energy%Quan3za3on%
: Standing%Waves%created%by%2%traveling%waves%in%opposite%direc3on;%Nodes%and%An3nodes%%
%(Sec3ons%17.2,%17.3,%Figs.%17.5,%17.6,%17.9)%
: The%energy:levels%of%an%atom%are%quan3zed%(Bohr%model)%because%the%electron%is%a%wave!%(classnotes)%
%%
• Beats%&%the%2nd$basic$tenet$of$QM:%Wave:Par3cle%Duality%
:% %Waves%can%behave%like%Par3cles%
o Consider%Beats%(Demo%with%tuning%forks)%(Sec3on%17.8).%
o Many%sinusoidal%waves%added%together%yield%a%wavepacket.%
o Time:dura3on%of%wavepacket%and%frequency%bandwidth%of%the%source%are%related.%
o Spa3al%extent%of%wavepacket%–%deBroglie%wavelength%(Sec3on%38.4%and%39.5)%
o Can%the%deBroglie%wavelength%of%an%electron,%or%of%an%atom,%equal%the%op3cal%wavelength?%
:% %Par3cles%can%behave%like%Waves%
o Consider%the%two:slit%interference%experiment%(Remember%the%“Fabric%of%Cosmos”%video?)%
o Electrons%interfere!%Demo:%Davisson:Germer%expt%
o Atoms%interfere!%New%state%of%Maber%–%Bose:Einstein%condensate%(1997,%2001%Physics%Nobels)%
%
• Diffrac3on%and%the%3rd$basic$tenet$of$QM:%Heisenberg%Uncertainty%Principle%(Sec.%39.6)%
: Waves%diffract,%i.e.,%bend%around%obstacles%
Defining%signature%of%waves!%
