Pressure Flashcards
Give the defintion of pressure along with it’s dimensions.
P = F/A
[P] = [N/m2] = [Pa], where Pa is the abbreviation of Pascals.
Einstein’s view of pressure: The frequency at which the particles bump into things.
How many Pascals is equivalent to 1 atm (atmospheric pressure)?
1.01325 x 105 Pa.
Give the pressure of air above you head.
With the only force acting on air is the gravitional force (mg),
P = δair·h·g
In physics and thermodynamics, an _____________________ is a thermodynamic equation relating state variables which describe the state of matter under a given set of physical conditions, such as pressure, volume, temperature (PVT), or internal energy.
Give an example of this equation.
equation of state.
The ideal gas law, PV = NKBT
Give the mathematical definition of subtend.
To take up the side opposite an angle or arc.
Ex. The arc length, S, subtends the angle θ in θ = S/r.
By analogy of θ = S/r, define a solid angle Ω in a sphere?
As well, what would be the solid angle subtended by the whole sphere?
Ω = A / r2,
4π
Give equivalent forms of PV = NkBT.
P = nkBT, where n = N/V (number density)
PV = nmRT, where nm = number of moles and R = NAkB
If we increase the mass of each particles but keep T and n the same, what will be the change in pressure? Assume that the gases obey the ideal gas law.
p(n,T) = nkBT
no change, since pressure is independent of mass.
Give the formula that governs the conversion of Kelvin to Celsius.
ºC = K - 273
Remember, the Kelvin temperature scale does not use the degree (°) symbol. The reason is because Kelvin is an absolute scale, based on absolute zero, while the zero on the Celsius scale is based on the properties of water.
The volume in the ideal gas law is a macroscopic property, but what would you consider n, number density, to be?
microscopic, the number of molecules per unit volume.
How is the number density related to finding the average distance between molecules?
it is it’s inverse.
V / N = n-1 , this is the volume per molecule.
One can assume that each molecule is a sphere, then
n-1 = 4πr3 / 3
What is the volume of a parallelepiped?
VParallelepiped = (u x v) · w = base x height,
where u & v are the base and w is the length of the parallelepiped.
How would you find the mass of a single atom from the periodic table?
Given the atomic mass per mole (given in every periodic table), divide by Avogadro number’s number.
Mass per atom = Atomic mass / NA
In general, a thermodynamic system can be fully described by a set of 3 thermodynamic variables (x, X, T), one of which shoud be temperature T. What would be the other two, x & X?
Intensive and Extensive variables.
Name a geometric application of the cross product.
The magnitude of the cross product of two vectors, that are not scalar versions of each other, is the area between the vectors.
