Physics 7B: Final Exam Review Spring 2010
Brian Henning
May 5, 2010
Problem I–some warmup questions
a) Discovering the positron
Shown in the figure is the track showing the discovery of the positron (the positron is the anti
electron; it has the same mass but opposite charge to the electron). A uniform magnetic field is
present and the positron crosses a piece of lead in the middle. The lead serves to slow down the
positron. In what direction is the positron going through the lead plate (you must show proof of
this)? What direction is the magnetic field?
b) PV diagram
Consider a cyclic process (represented by the circle on the
PV
diagram) with 0.4 mole of ideal gas.
Calculate the amount of heat transferred to the gas between the minimum and maximum volumes.
1
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c) Compressibility
Isothermal compressibility,
κ
T
, is defined as the ratio of the change in volume for a given change
in pressure to the total volume at constant temperature:
κ
T
≡ −
1
V
∂V
∂P
(constant temperature)
where the minus sign reflects that if at constant temperature we increase pressure and therefore
decrease volume we get a positive compressibility.
1. Find the isothermal compressibility for an ideal gas
2. Find the isothermal compressibility for a hard core gas that obeys the equation of state
P
(
V
−
bN
) =
NkT
where
b >
0. Show that in the limit of infinite volume, the compressibility
approaches that of an ideal gas. Why is this physically?
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 Spring '08
 ZETTLE
 Thermodynamics, Electron, TA, Fundamental physics concepts, inner cylinder

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