052516 week11 quantum3

Learning ObjectivesLearning Objectives• Who was involved?Who was involved?• Which experiments were used to help Which experiments were used to help

us understand?us understand?• What are atomic line spectra?What are atomic line spectra?• Which models were used to represent Which models were used to represent

the atom?the atom?• Which equations are fundamental?Which equations are fundamental?• Which ones are handy to know?!Which ones are handy to know?!• What have been the successes of What have been the successes of

quantum theory?quantum theory?• What are the future applications?What are the future applications?

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Albert Einstein 1879-1955Albert Einstein 1879-1955

• We believe in the We believe in the possibility of a theory possibility of a theory which is able to give a which is able to give a complete description complete description of reality, the laws of of reality, the laws of which establish which establish relations between the relations between the things themselves things themselves and not merely and not merely between their between their probabilities ... GOD probabilities ... GOD DOES NOT PLAY DICE.DOES NOT PLAY DICE.

Niels Bohr 1885-1962Niels Bohr 1885-1962

• Einstein, DON'T TELL Einstein, DON'T TELL GOD WHAT TO DO!GOD WHAT TO DO!

• Those who are not Those who are not shocked when they shocked when they first come across first come across quantum mechanics quantum mechanics cannot possibly have cannot possibly have understood it.understood it.

Werner Heisenberg 1901-1976Werner Heisenberg 1901-1976• We have to remember We have to remember

that what we observe that what we observe is not nature itself but is not nature itself but nature exposed to our nature exposed to our method of method of questioning. questioning.

• I, at any rate, am I, at any rate, am convinced that HE IS convinced that HE IS NOT PLAYING AT NOT PLAYING AT DICE.DICE.

Erwin Schroedinger 1887-1961Erwin Schroedinger 1887-1961

• I do not like it, and I I do not like it, and I am sorry I ever had am sorry I ever had anything to do with it.anything to do with it.

• Had I known that we Had I known that we were not going to get were not going to get rid of this damned rid of this damned quantum jumping, I quantum jumping, I never would have never would have involved myself in this involved myself in this business!business!

Prince Louis de BrogliePrince Louis de Broglie1892-19871892-1987

• Electrons should not Electrons should not be considered simply be considered simply as particles, but that as particles, but that frequency must be frequency must be assigned to them also.assigned to them also.

(1929, Nobel Prize (1929, Nobel Prize Speech)Speech)

Max Planck 1858-1947Max Planck 1858-1947

• Physics is finished, Physics is finished, young man. It's a young man. It's a dead-end streetdead-end street..

(from an unknown (from an unknown teacher to Planck teacher to Planck

considering Physics at considering Physics at the turn of the 20the turn of the 20thth

century!)century!)

THE ‘ULTRAVIOLET CATASTROPHE’

1900 - RayleighThis was a CLASSICAL prediction, first made in the late 19th century, that an IDEAL BLACK BODY at thermal equilibrium will emit radiation with INFINITE POWER.

Max Planck resolved this issue by postulating that electromagnetic energy did not follow the classical description, but could only oscillate or be emitted in DISCRETE PACKETS OF ENERGY proportional to the frequency. He called these packets ‘QUANTA’.

hE Note: sJxh .10626.6 34

THE PHOTOELECTRIC EFFECT

1905 - Einstein

The emission of electrons from a surface (usually metallic) upon exposure to, and absorption of, electromagnetic radiation.

The photoelectric effect was explained mathematically by Einstein who extended the work on QUANTA as developed by Planck.

hKE

MILLIKAN’S OIL DROP EXPERIMENT

1909 - Robert Millikan

This experiment determined the magnitude of the electronic charge, and that it was QUANTISED.

This value is approximately

Cx 19106.1

Note: An electron volt (eV) is the amount of energy it takes to accelerate one electron through a potential of one volt. Thus, 1eV Jx 19106.1

DE BROGLIE WAVELENGTH

Prince Louis de Broglie - 1932

De Broglie discovered that all particles with momentum have an associated wavelength.

mvh

ph

What is the wavelength of a human being, assuming he/she weighs 70 kg, and is running at 25 m/s?

NUCLEAR ATOM STRUCTURES

1898 - Thomson

1911 -Rutherford

1913 - Rutherford/Bohr

Atomic Line Spectra

• General expression:General expression:

• Lyman:Lyman: n>1 n>1 (ultraviolet)(ultraviolet)

• Balmer:Balmer: n>2 n>2 (visible)(visible)

• Paschen:Paschen: n>3 n>3 (infrared)(infrared)

• Brackett:Brackett: n>4 n>4 (infrared)(infrared)

• Pfund:Pfund: n>5 n>5 (infrared)(infrared)

2nhcREn

22

1111

nR

22

1211

nR

22

1311

nR

22

1411

nR

22

1511

nR

SUMMARY OF IMPORTANT EQUATIONSSUMMARY OF IMPORTANT EQUATIONS

• Energy and frequency:Energy and frequency:

• The photoelectric effect:The photoelectric effect:

• De Broglie wavelength:De Broglie wavelength:

• Angular frequency:Angular frequency:

hchE

hKE

mvh

ph

f 2

Equations of interest Equations of interest (non-examinable!)(non-examinable!)• Planck’s constant:Planck’s constant:

• Wave vector:Wave vector:

• Schroedinger:Schroedinger:

2h

2

k

V

mti 2

2

2

Richard Feynman 1918-1988Richard Feynman 1918-1988

• Anyone who has not Anyone who has not been shocked by been shocked by quantum physics has quantum physics has not understood it. not understood it.

• The word 'quantum' The word 'quantum' refers to this peculiar refers to this peculiar aspect of nature that aspect of nature that goes against goes against common sense.common sense.

Groucho Marx 1890-1977Groucho Marx 1890-1977

• Very interesting Very interesting theory - it makes no theory - it makes no sense at allsense at all!!

QUANTUM THEORYQUANTUM THEORY

UsesUses

• LASERsLASERs• SemiconductorsSemiconductors• TransistorsTransistors• LEDLED• Night Vision Night Vision

GogglesGoggles• CCDCCD• MRI / PETMRI / PET

ExplainsExplains

• TunnellingTunnelling• Radioactive decayRadioactive decay• Periodic table Periodic table

(Pauli Exclusion (Pauli Exclusion Principle Principle

explanation to explanation to Mendeleev’s chart)Mendeleev’s chart)

THE FUTURE OF QUANTUM?THE FUTURE OF QUANTUM?

• Dot LASERsDot LASERs• Logic gatesLogic gates• ComputingComputing• Cryptography / EncryptionCryptography / Encryption• CloningCloning• TeleportationTeleportation