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I can convert the optics to non-reversible by spreading a thin layer of dust on top. Now both systems are non-reversible and both allow higher temperatures? Or

by DenisM 8y ago

I can convert the optics to non-reversible by spreading a thin layer of dust on top. Now both systems are non-reversible and both allow higher temperatures? Or are we looking at a particular kind of non-reversibility?

whatshisface 8y ago
Covering the lens with dust would let you light a fire. The dust will warm slightly above ambient temperature in the lens' shadow, so you can use it to power a Carnot engine that winds up a spring that is then released to rub a twig against a log.
- AlexCoventry 8y ago
  This is genius.
schoen 8y ago
I think the thermodynamics argument is that only non-reversible systems cause energy to flow from a lower-temperature source to a higher-temperature destination, not that all non-reversible systems do so. For example, if you set up a solar panel that directly feeds a resistor, you have a dissipative system that's unlikely to get hotter than the sun. However, a solar panel array and/or battery could conceivably power a fusion reaction that does get hotter than the sun.
- DenisM 8y ago
  >if you set up a solar panel that directly feeds a resistor, you have a dissipative system that's unlikely to get hotter than the sun. I guarantee you this can be done. Arc welding [1] goes to many thousands of degrees, up to 20,000C. A square mile of solar panels will most certainly give me enough energy to power an arc welder. In fact I will probably will get away with just 100kw of pwoer, so 500 panels give or take. [1] https://hypertextbook.com/facts/2003/EstherDorzin.shtml https://hypertextbook.com/facts/2003/EstherDorzin.shtml
  - Dylan16807 8y ago
    Okay, sure, as long as you're not trying to say this contradicts the post. "A resistor" was just an example of how you could waste the power and not get much heat.
Isobit 8y ago
Wouldn't this layer of dust also stop the lense from working normally? If I understand the other commenters here, it's not just about reversibility, but "useful energy" loss - with lenses you are not paying the needed "efficiency tax" to achieve higher temperatures than the source.

by DenisM 8y ago

whatshisface 8y ago

Covering the lens with dust would let you light a fire. The dust will warm slightly above ambient temperature in the lens' shadow, so you can use it to power a Carnot engine that winds up a spring that is then released to rub a twig against a log.

AlexCoventry 8y ago
This is genius.

schoen 8y ago

I think the thermodynamics argument is that only non-reversible systems cause energy to flow from a lower-temperature source to a higher-temperature destination, not that all non-reversible systems do so. For example, if you set up a solar panel that directly feeds a resistor, you have a dissipative system that's unlikely to get hotter than the sun. However, a solar panel array and/or battery could conceivably power a fusion reaction that does get hotter than the sun.

DenisM 8y ago
>if you set up a solar panel that directly feeds a resistor, you have a dissipative system that's unlikely to get hotter than the sun. I guarantee you this can be done. Arc welding [1] goes to many thousands of degrees, up to 20,000C. A square mile of solar panels will most certainly give me enough energy to power an arc welder. In fact I will probably will get away with just 100kw of pwoer, so 500 panels give or take. [1] https://hypertextbook.com/facts/2003/EstherDorzin.shtml https://hypertextbook.com/facts/2003/EstherDorzin.shtml
- Dylan16807 8y ago
  Okay, sure, as long as you're not trying to say this contradicts the post. "A resistor" was just an example of how you could waste the power and not get much heat.

Isobit 8y ago

Wouldn't this layer of dust also stop the lense from working normally? If I understand the other commenters here, it's not just about reversibility, but "useful energy" loss - with lenses you are not paying the needed "efficiency tax" to achieve higher temperatures than the source.