AZING!What is the Polytopic Index for a given set of Pressure and Volume values?

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Discussion Overview

The discussion revolves around determining the polytropic index (n) from given pressure (P1, P2) and volume (V1, V2) values. Participants explore methods to isolate n using logarithmic relationships and the polytropic equation.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant presents an equation based on the polytropic process, suggesting that P1V1^n = P2V2^n can be used to find n.
  • Another participant proposes using logarithmic manipulation to isolate n, indicating that if xn = k, then ln(xn) = ln(k).
  • A participant expresses uncertainty about how to isolate n after attempting to set up the logarithmic equation.
  • There is a request for help due to an upcoming test, indicating urgency in resolving the problem.
  • One participant reiterates the logarithmic approach, showing the steps taken but remains unsure about isolating n correctly.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the method to isolate n, and multiple approaches are suggested without agreement on a definitive solution.

Contextual Notes

There are unresolved steps in the mathematical manipulation, and participants express uncertainty regarding the isolation of n, indicating potential limitations in their current understanding of the logarithmic relationships involved.

tsukuba
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Homework Statement


Hello, I came across a problem where the polytropic index is not given but I've been given P1, P2, V1 and V2.

P1V1 = P2V2 (130kPa)(0.007m3)n = (100kPa)(0.08637m3)n ----> n=1.249

Homework Equations


PVn=constant
I was thinking I would have to use log to figure out n maybe?

The Attempt at a Solution


haven't been able to work it out backwards. Need your help please!
 
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tsukuba said:
I was thinking I would have to use log to figure out n maybe?
If xn = k then ln(xn) = ln(k)AM
 
the value of n is not given. I just put it there because but what if it was
xn = ?
solving for n
 
somebody helpppp
I have a test tomorrow
 
I came to this but now I am not sure how to isolate for n

ln(130) n*ln(0.07) = ln(100) n*ln90.08637)
 
tsukuba said:
I came to this but now I am not sure how to isolate for n

ln(130) n*ln(0.07) = ln(100) n*ln90.08637)

P_1V_1^n = P_2V_2^n
\frac{P_1}{P_2} = \left(\frac{V_2}{V_1}\right)^n
\ln(P_1)-\ln(P_2) = n(\ln(V_2) - \ln(V_1))

Can you work it out from there?

AM
 

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