![Page 1: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/1.jpg)
Failures of Classical Physics and the
Birth of Quantum Mechanics
Mark Van Raamsdonk
![Page 2: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/2.jpg)
The classical description of light
Light, X-rays, microwaves, radio waves, are all examples of ELECTROMAGNETIC RADIATION:
Oscillating electric field
Oscillating magnetic field
James Clerk Maxwell 1864
![Page 3: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/3.jpg)
Properties of Light
Colour: determined by wavelength
Intensity: determined by amplitude
![Page 4: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/4.jpg)
Light carries energy
Energy Intensity Amplitude Squared
![Page 5: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/5.jpg)
Q: How can we make some electromagnetic radiation?
![Page 6: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/6.jpg)
Q: How can we make some electromagnetic radiation?
A: Shake some charges
Power radiated acceleration squared
![Page 7: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/7.jpg)
Failures of classical physics I
”Planetary” picture of atom:
Electrons orbiting around nucleus
Sounds okay, but...
![Page 8: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/8.jpg)
Orbiting charge would produce EM radiation
This carries away energy
Electron losing energy spirals into nucleus
All matter as we know it ceases to exist in 10-10s.
![Page 9: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/9.jpg)
Failures of classical physics II
Light from any source is a combination of wavelengths and intensities.
19th century physicists completely failed to explain observed spectrum of light from hot objects
![Page 10: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/10.jpg)
Even more mysterious: spectrum of light from gases of pure elements
Hydrogen Helium Neon
![Page 11: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/11.jpg)
The photoelectric effect
Observation: electrons ejected from metalwhen light is turned on
![Page 12: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/12.jpg)
The photoelectric effect: explained
Electrons trapped in metal(attracted to positive nuclei)
Can free them if we provide enough energy
Energy carried by light can be transferred to electrons
BUT: we only see the effect for certain colours!?
![Page 13: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/13.jpg)
Very intense red light:No electrons
Feeble blue light:Electrons emitted
![Page 14: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/14.jpg)
Einstein to the Rescue
Einstein’s idea: light made of “photons” =lumps with energy inversely proportional to wavelength
![Page 15: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/15.jpg)
Einstein’s explanation
Electrons can only absorb energy from individual photons
Only light with short enough wavelength has photons with enough energy to eject an electron
![Page 16: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/16.jpg)
Einstein’s Only Nobel Prize
Quantitative prediction (1905): maximum kinetic energy of ejected electrons increases linearly with inverse of wavelength (photon energy)
Experimental verification by Milliakan in 1915
Nobel prize for Einstein in 1921
![Page 17: Failures of Classical Physics and the Birth of Quantum ...admin.triumf.ca/docs/seminars/Sem3154321373-26928... · Failures of classical physics II Light from any source is a combination](https://reader030.vdocuments.us/reader030/viewer/2022040402/5e8386e6e6c14f690b379ecb/html5/thumbnails/17.jpg)
Today: can use photoelectric effect to “see” individual photons