Understanding Vapor Pressure Laws for Astrophysics

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SUMMARY

The discussion centers on the vapor pressure law used in astrophysics, specifically the equation log(pressure) = A - (B/T), where A is 10.6 and B is 13500. The pressure is measured in dynes/cm², and the logarithm is confirmed to be natural (base e). The user is implementing this equation in MATLAB as pressure = 10^(A - (B/T)), but seeks clarification on the units of A and B, as well as the appropriate logarithmic base. The closest reference for this formula can be found in the vapor pressure resources provided by CIRES.

PREREQUISITES
  • Understanding of vapor pressure laws
  • Familiarity with MATLAB programming
  • Knowledge of thermodynamic units (Pascal, dynes/cm²)
  • Basic logarithmic functions and their applications
NEXT STEPS
  • Research the derivation and applications of the Clausius-Clapeyron equation
  • Learn how to implement logarithmic functions in MATLAB
  • Explore the relationship between vapor pressure and temperature for different substances
  • Study the conversion between dynes/cm² and Pascal for pressure measurements
USEFUL FOR

Astrophysics students, researchers in thermodynamics, and MATLAB users interested in modeling vapor pressure phenomena.

ZachWeiner
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So, I'm new to astrophys, and I'm having trouble making a model because I don't think I understand an equation. It's a vapor pressure law, and it says it takes the form of

log(pressure) = A-(B/T)

T is in kelvins, A is 10.6, and B is 13500.

Apparently pressure ends up being dynes/cm^2.

So, first off, I don't know the units of A or B, or whether log is base ten or base e.

In MatLab, I'm saying pressure = 10^(A-(B/T))

Because I don't understand the equation, I don't know if that makes sense or not! Please help!
 
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You can find many vapor pressure formulae (for water) here:
http ://cires.colorado.edu/~voemel/vp.html
Equation [17] there looks the closest to your formula.
Then the logarithm is natural and P is measured in Pascal.
However, you may have the logarithm on the base 10 and pressure in hectoPascals.
Pressure of what are you interested in? Is it actually water?
 

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