I An experiment against the second law of thermodynamics

[jbriggs444]

I would say this "semi mirror" doesn't even have to be perfect as you describe it.
Any "passive" mirror that transmits a bit more in one direction and reflects a bit more in the other should be in conflict with the 2nd law.

By "passive" I mean that it doesn't require energy input.

If you just imagine two large, plane surfaces at the same temperature and then you put such a mirror between them the one surface would heat up and the other would cool down.

Do you agree?

If the semi-mirror were imperfect (absorbed some fraction of the radiation impinging on it) then the concern would arise about how it would re-emit that radiation. So now we have that complexity to contend with.

 

[Philip Koeck]

If the semi-mirror were imperfect (absorbed some fraction of the radiation impinging on it) then the concern would arise about how it would re-emit that radiation. So now we have that complexity to contend with.

I agree. That's why I only considered transmission and reflection. The semi-mirror shouldn't absorb.

 

[Vanadium 50]

If you require V to be identically zero, you require the thermal noise to be zero as well, i.e. T = 0.

If you have a resistor at T > 0 and a diode at T = 0, you have a heat engine. Of course you can extract work.

 

[lerus]

Thank you for your answer.
I agree, but just $V=0$ is not enough to extract work. It's a combination of $V=0$ and $I=0$ that extracts work.
Is it correct that ability to extract work from thermal noise contradicts to the second law of thermodynamics?

And one more question, sorry. Does superconductor produce thermal noise? If it doesn't then we have one half of prefect diode and $T>0$. Probably somebody else could figure out how to create the other half of perfect diode :).

 

[Vanadium 50]

Again, you are discussing a heat engine. You extract work by having part of it at one temperature and part at another. The fact that the components are electrical and not mechanical is irrelevant.

Imagining one part kept at absolute zero, even implicitly, gets you a Perpetual Motion Machine. We do not discuss these here, but armies of people have tried to make them, and have them "almost work - as soon as I get this last part right."

 

[lerus]

Again, you are discussing a heat engine. You extract work by having part of it at one temperature and part at another. The fact that the components are electrical and not mechanical is irrelevant.

Imagining one part kept at absolute zero, even implicitly, gets you a Perpetual Motion Machine. We do not discuss these here, but armies of people have tried to make them, and have them "almost work - as soon as I get this last part right."

I'm sorry, probably I was not able to ask question properly. I didn't want to suggest Perpetual Motion Machine. I wanted to ask - is it possible to determine which volt-ampere characteristics are allowed by 2nd law of thermodynamics and which are not?

 

[Vanadium 50]

is it possible to determine which volt-ampere characteristics are allowed by 2nd law of thermodynamics and which are not?

For the third time, no. Voltage and current are not the only two relevant quantities. Temperature is as well. You cannot sensibly discuss thermodynamics and ignore temperature.

 

[lerus]

For the third time, no. Voltage and current are not the only two relevant quantities. Temperature is as well. You cannot sensibly discuss thermodynamics and ignore temperature.

Thank you, I think I understood at last. Energy will flow from hotter body to colder, as it should.
If temperature of one of the bodies is $0$, this body will be able to extract energy from any other body. It means that we created Perpetual Motion Machine, which is not possible.
Thank you for being so patient.