- #1
curiousvortex
- 1
- 0
Homework Statement
http://i.imgur.com/2WKCR.jpg
Homework Equations
Potentially: L(final) = L[1 + tau/(YA) + alpha(T - To)]
The Attempt at a Solution
Frankly I have no idea where to begin.
rude man said:Well, you left out quite a few steps but it's right.
BTW my textbook uses "A" instead of "F" for the Helmholz function. And, if I may suggest, don't use t for temperature. Use T. t is almost always time.
rude man said:Sorry, that got by me completely.
You gave an equation, whence did it come? How about starting from the 1st law?
[itex]\delta F=\delta U-(\delta T)S-T(\delta S)=-S\delta T+t\delta l [/itex].francesco85 said:I'm sorry, but I think that I don't understand: let me go into the details of the derivation, also covering well-known thermodynamics result; is the equation you are talking about
[itex]\delta U=T\delta S+t\delta l[/itex] ?
If so, then I think that this is just the first law for the system we are talking about (with [itex]\delta[/itex] I mean an infinitesimal change; well, to be rigorous, an infinitesimal reversible change); for every thermodynamic system we are supposed to have a function of state U (the internal energy) and to be able to define an ordered work ([itex]t\delta l[/itex]) and a disordered work ([itex]T\delta S[/itex]); then, by definition, I define
[itex]F=U-TS[/itex] and then
[itex]\delta F=\delta U-(\delta T)S-T(\delta S)=-S\delta T+t\delta l [/itex].
Did I understand what you have asked or did you mean something else?
rude man said:[itex]
You can do without that concept by
dU = dQ + dW 1st law, dw > 0 here.
dU = TdS + dW
dW = tdL
so dU = TdS + tdL
dF = dU - TdS - SdT
dF = TdS + tdL - TdS - SdT
dF = tdL - SdT
and the partials fall out as you indicated.
rude man said:[itex]\delta F=\delta U-(\delta T)S-T(\delta S)=-S\delta T+t\delta l [/itex].
Maybe I'm being picky but
dU - SdT -TdS = -SdT + tdL was not obvious to me. Admittedly I did not identify 'orderd' and 'disorderd' work as tdL and TdS respectively. In fact I don't remember coming across those terms at all except that certainly they make sense, qualitatively at least.
A thermodynamic system is a physical system that is studied under the principles of thermodynamics, which is the science of energy and its transformations. It can be a closed system, where no energy or matter is exchanged with its surroundings, or an open system, where energy and matter can be exchanged.
A wire can be considered as a part of a thermodynamic system because it is a physical object that has properties such as temperature and energy that can be studied and analyzed using the principles of thermodynamics.
A wire is significant in thermodynamics because it plays a crucial role in energy transfer and conversion. Wires are commonly used to carry electricity, which is a form of energy, and they also have properties that are affected by thermodynamic processes, such as electrical resistance and heat conduction.
The thermodynamic system of a wire can be described by analyzing its properties, such as temperature, energy, and entropy, and how they change under different thermodynamic processes. This can help in understanding the behavior of the wire and its role in energy transfer and conversion.
Yes, the thermodynamic system of a wire can be affected by external factors such as temperature, pressure, and the presence of other substances. These factors can change the properties of the wire and impact its behavior in thermodynamic processes.