Physics of Astronomy Tuesday, winter week 7 21 Feb'06

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Physics of AstronomyTuesday, winter week 7 (21
Feb.06)
Math-A Giancoli Ch.78 Work and
Energy Discuss rotational dynamics lab Math-B
Giancoli 11, Raff Ch.11.2.1-3 Intro to QM HW
setup Dr. Neal Hurlburt visits Wednesday lunch
discussion 100 here Looking ahead quiz this
Thus.
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Relationship between force and work/energy
Examples of energy Work done force .
displacement in the same direction Dot product
product of PARALLEL components of
vectors Do Ch.7 (p.171) Forces Work 4, 6,
7, Dot products 21, 25
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7-3 Work done by a varying force
Example Spring obeys Hookes law F
-kx Do Ch.7 (p.172) F(x) 31-34, 39
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7-4 Work Energy
Loss of potential energy?work done?increase in
Kinetic energy - DU ? W ? DK Ex falling mass
in last weeks experiment Ch.7 (p.173)
41, 46, 49, 52, (p.175) 65,
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Ch.8 Energy conservation

• Conservative force
• Work done doesnt depend on path taken (curl x F
  0)
• Net work done around a closed path 0
• potential energy U depends only on x, and Fx
  -dU/dx
• Etot K U constant (conservation of
  mechanical energy)
• Gravity and Felec are conservative Friction and
  Fmag are not
• Ch.8 (p.200) 7,9, 10, 16, 17, (p.202) 32, 36(a),
  41, 42-47, 73, 82, 89, 93

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Gravitational potential energy and force
Near earth far from Earth Force
F Potential energy U
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Ch.8-8,9 Energy diagrams and Power
Power rate of change of Energy P
dE/dt Minimum energy stable state
(F0) Ch.8 (Power, 203) 57, 59, 62, 65,
67, (Diag) 68-71, 94-97
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Phys.B Raff 11.2.1-3 Introduction to Quantum
Mechanics Blackbody radiation

• Blackbodies were carefully studied in labs in
  late 1800s
• Rayleigh-Jeans theory explained long-wavelength
  tail l 1/T (Wiens law)
• Ultraviolet catastrophe at short l!

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Plancks quantization of photon energy

• Plancks phenomenological relation fit, but why?
• Three weeks later, Plancks revolutionary
  explanation

Probs. 11.7 and 11.8 Long and short-l limits of
blackbody radiation.
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Blackbody radiation notation
Q energy (joules) energy density u
Q/volume Ql dQ/dl (J/m) energy density
/wavelength u(T, l) Ql /volume Power
dQ/dt (J/s) emissive power dP/dl /
area Luminosity Power/area
Prob. 11.9 Find energy maximum where du/dl 0
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Photons as particles Photoelectric effect
Photons can knock electrons out of metal, if they
can overcome the binding energy to the metal, or
work function W. Ephoton KEelectron binding
energy hn KEmax W Brighter light
yields more electrons. Shorter wavelength light
yields more energetic electrons. Even weak
light beam of single photons can release e.
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Atomic models