32102_Lec29-Quantum Atom

32102_Lec29-Quantum Atom - The Modern Quantum Atom Thenucle...

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The Modern Quantum Atom The nucleus and the discovery of the neutron What are electron-volts ? The Quantum atom Announcements HW#8 posted (sorry) Prof. Artuso giving Monday’s class. I may allow a calc. For Exam 3
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Positively Charged Nucleus Corpuscles (Electrons) Electrons circle the nucleus due to the Coulomb force Rutherford’s Picture of the Atom ~10 -14 m ~10 -11 m Rutherford Scattering: http://galileoande instein.physics.virginia.edu/more_stuff/Applets/rutherford/rutherford.html This model was inspired by the results of scattering alpha-particles off of heavy nuclei (like gold, silver, etc). See previous lecture.
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James Chadwick and the Neutron Awarded the Nobel Prize in 1935 1891-1974 Circa 1925-1935 Performed a series of scattering experiments with α -particles (recall a particles are He nucleus) , 4 2 He + 9 Be 12 C + 1 0 n Applying energy and momentum conservation he found that the mass of this new object was ~1.15 times that of the proton mass. Picked up where Rutherford left off with more scattering experiments… (higher energy though!) Chadwick postulated that the emergent radiation was from a new, neutral particle , the neutron.
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***Electron-Volts (eV)*** When talking about subatomic particles, and individual photons, energies are very small (~10 -12 or smaller). It’s cumbersome to always deal with these powers of 10. We introduce a new unit of energy , called the electron-volt (eV). An [eV] is equivalent to the amount of energy a single electron gains when it is accelerated across a voltage of 1 [V]. Your TV tube accelerates electrons using 20,000 [V] = 20 [kV]. 0 [kV] -20 [kV] 10[J] 0 [J] 1 kg GPE 1 m 0 [V] -20 [kV] + - Electric Potential
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More on [eV] How much energy does an electron gain when it is accelerated across a voltage of 20,000 [V] ? E = 20,000 [eV]
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This note was uploaded on 12/13/2010 for the course PHY 8 taught by Professor D during the Spring '10 term at MIT.

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32102_Lec29-Quantum Atom - The Modern Quantum Atom Thenucle...

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