/sci/ - Science & Math

[Anonymous No.3053987]

I don't know much about physics, /sci/, but aren't these examples of Carnot Cycles? Just finished up an online quiz, and I chose that all of them were Carnot Cycles, yet none of them are? Aren't those like... actual depictions of Carnot Cycles?

[Anonymous No.3054005]

If I recall correctly, pressures and volumes are not constant in Carnot cycles, they have 2 adiabatics and 2isotherms

[Anonymous No.3054020]

>>3054005
Right, but they're not constant in these pictures, are they? I know net internal energy is zero, and change in temperature and volume are equal, but these aren't constants? I just googled Carnot Cycle and checked images to make sure I wasn't crazy, and I mean... that's all that comes up. I'mma check wiki to make sure, but yeah.

[Anonymous No.3054045]

>>3054020
1 is Carnot, 4 isnt, the others arnt completely isothermal and isobaric (you can see by the curves)

[Anonymous No.3054051]

>>3054020

The equation for isotherm process is (ideal gas)

<div class="math">PV= constant</div>

For adiabatic

<div class="math">PV^{\gamma} = constant</div>

gamma is the Poisson coefficient

The product is constant, so none of them can be constant

The cycle 2 could be a Carnot one but I dont know is the lower line is totally horizontal

[Anonymous No.3054058]

>>3054020
in all of those pictures where there is one line where P is constant. in the carnot process, the most effective process there is, there is no line with constant P.

In the carnot process, what is constant is always energy related:
One time Q is constant (adiabatic process), so no heat flow dQ. and therefore also dS=dQ/T=0.
And the other time T is constant, so dT=0, which means dU=0, since for ideal gas U=U(T), or more precisely
U(T)=c·T=b·pV, where c and b are some constants.

So if you see a process where V or P is constant, then it's not good for the energy.

[Anonymous No.3054069]

>>3054020
in all of those pictures there is one line where P=constant. But in the carnot process (the most effective process there is) there is no line with constant P.

In the carnot process, what is constant is always energy related:
One time Q is constant (adiabatic process), so no heat flow dQ. and therefore also dS=dQ/T=0.
And the other time T is constant, so dT=0, which means dU=0, since for ideal gas U=U(T), or more precisely
U(T)=c·T=b·pV, where c and b are some constants.

So if you see a process where V or P is constant, then it's not good for the energy.

[Anonymous No.3054081]

>One time Q is constant
I should at that this is an informal statement meaning dQ=0, since there is no "heat-function Q".
The enthalpy H is what comes closest to a heat function.

[Anonymous No.3054090]

<span class="math">
http://www.youtube.com/watch?v=1DUNPs6meuY&t=5m20s
[/spoiler]