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Welcome back
to 8.033!
Relativistic dynamics summary:
MIT Course 8.033, Fall 2006, Lecture 12Max Tegmark
Today’s topics:• Atomic, nuclear & particle physics
• Parallel & transverse acceleration & force
• Particle accelerators
FOCUS OF PARTICLE PHYSICS COMPONENT OF 8.033:
1) Give you basic overview of atomic, nuclear & particle physics sothat you can
1) Better see the big picture
2) Get more out of popular talks and articles
3) Pass the “cocktail party test”
2) Apply two core relativity results:
1) Mass-energy unification
2) Energy-momentum conservation
Atomic physics
Alpha p;~rtic:
Gold foil
Gold FoilRadioactive substance
Alpha particles
Figure by MIT OCW.
Image courtesy of Wikipedia.
#118 just confirmed!
Spectral line experiment
Figure by MIT OCW.
Image courtesy of NASA.
Image courtesy of NASA.
Figure by MIT OCW.
Emission spectrum of hydrogen:
Emission spectrum of iron:
Image courtesy of Wikipedia.
Image courtesy of Wikipedia.
How do we know what stars
are made of?
Proton
n = 4n = 3
n = 2
n = 1
Figure by MIT OCW.
Absorption Emissionba
n = 2n = 3
Figure by MIT OCW.
122 n
m 103 n
m 97.3
nm95.0 nm 93.8 nm
656 nm486 nm
434 nm410 nm
1875 nm
1282 nm
1094 nm Paschen series (infrared)
n = 5
n = 4
n = 3
n = 2
n = 1
n = 6
Lyman series (ultraviolet)
Balmer series (visible)
Figure by MIT OCW.
Photons
Figure by MIT OCW.
Photoelectric effect
Figure by MIT OCW.
Photoelectric effectLenard 1902
Figure by MIT OCW.
Photoelectric effect
Einstein's model was that
- the photon carries energy hv
- a certain work We is required to liberate an electron from the metal
This explained both of Lenard's 1902 observations:
- light with frequency hv < We liberates no electrons at all
- light with frequency hv > We liberates electrons with kinetic energy hv - We.
- increasing the intensi ty of the light (the photon flux) didn't affect the existence of liberated electrons or their kinetic en- ergy
Bottom line: we can treat the photon as just another particle.
(PS6, problem 6)
The linear increase in electron kinetic energy shows that whatever is ejecting them has energy proportional to frequency.
The slope of the curve gave the constant of proportionality, which we now call Planck’s constant, h.
Image courtesy of Wikipedia.
(PS6, problem 4)
Nuclearphysics
Nuclear physics terminology
The atomic number Z of a nucleus is its number of protons.
The atomic weight A of a nucleus is its number of nucleons (protons + neutrons) .
Z determines the name of the element (its order in the periodic table).
Nuclei with same Z and different A are said to be different isotopes of the same element.
Notation example: ~e~~ means Z = 26 (iron) and A = 56.
The mass excess for a nucleus is mo - A amu, i. e., its rest mass minus the number of nucleons times amu.
By this definition, the mass excess of c12 is zero.
(PS6, problem 1)Proton
n = 4n = 3
n = 2
n = 1
Figure by MIT OCW.
• mn ≈ 939.6 MeV (udd)• mp ≈ 938.3 MeV (uud) • mu ≈ 4 MeV• md ≈ 7 MeV• Electromagnetic ≈ 1.7 MeV• So mostly glue!
Image courtesy of the National Nuclear Data Center.
FusionFission
Image courtesy of Wikipedia.
Brought to you by Tom Lehrer
