- #1

Greger

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does this look right?

for the quasistatic case you can use thermodynamics to find the temperature at any time,

for the other case you have to use dU=dW and so on since its not quasistatic

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- Thread starter Greger
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- #1

Greger

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- 0

does this look right?

for the quasistatic case you can use thermodynamics to find the temperature at any time,

for the other case you have to use dU=dW and so on since its not quasistatic

- #2

ehild

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does this look right?

for the quasistatic case you can use thermodynamics to find the temperature at any time,

for the other case you have to use dU=dW and so on since its not quasistatic

It is correct for the constant external pressure. But what is the final temperature in the quasi-static case? It is true that T

ehild

- #3

Greger

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so the quasistatic case should be:

T

for some reason i forgot that the pressure was changing in that case as well,

this makes more sense, in the quasistatic case you can find the state of the system at any point in terms of the state variables, and P is one of those too!

thanks ehild =]

- #4

ehild

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Can you show what you got? Just to complete the solution, so as other people learn from it.

ehild

ehild

- #5

Greger

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T

under constant pressue:

T

- #6

ehild

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T_{f}=P_{f}V_{f}/(NK_{B})

under constant pressue:

T_{f}=2P_{ex}(Vi-Vf)/3Nk_{B}+ Ti

Well, it is not the solution yet. You need to give T

ehild

- #7

Greger

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do you mean something like

where gamma is the ratio of heat capacities under constant pressure / volume?

- #8

ehild

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Yes. But you can combine it with the ideal gas law to give an equation between V and T.

ehild

ehild

- #9

Greger

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TV^(gamma - 1)=constant

PV^gamma = const

but wouldn't mucking around with these and introducing them into my problem make it like

Tf=PfVf/(NKB)=P

using λ as gamma

PV^gamma = const = C say

Tf=CV

then i have this unknown constant C

- #10

ehild

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yea there's afew like

TV^(gamma - 1)=constant

That is a good start. You can find that constant as you know the initial volume and temperature:

T

From the equation for the internal energy you can see that it is a mono-atomic gas, so you know Cv, and you also know the relation between Cv and Cp. What is γ-1 then?

ehild

- #11

Greger

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Tf= Ti(Vf Vi)^(γ-1)

for γ=Cp/Cv

Tf= Ti(Vf Vi)^(Cp/Cv-1)

is that kind of what you mean?

- #12

ehild

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Tf= Ti(Vf Vi)^(γ-1)

for γ=Cp/Cv

Tf= Ti(Vf Vi)^(Cp/Cv-1)

is that kind of what you mean?

Yes, but you made a little error:

T

And you know the numerical value of Cp/Cv what is it?

ehild

- #13

Greger

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T

T

thanks ehild

- #14

ehild

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It is the SOLUTION now

ehild

ehild

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