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# Example for laws of thermodynamics

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During the first oil crisis of the early 1970s, a business entrepreneur placed an expensive full-page advertisement in the New York Times, appealing to "the ingenuity of the American people." He offered a cash reward to any inventor who could "raise the temperature of a metal rod by cooling a second rod" and then "generate power by tapping the difference in temperatures."

Use your knowledge of thermodynamics to explain why nobody ever won the reward. Be specific.

https://brainmass.com/physics/first-law-of-thermodynamics/example-laws-thermodynamics-460521

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The laws of TD state that heat would flow from a hotter rod to a cooler one. It is not spontaneous to cool a rod by making another rod hotter without supplying some external energy. Even if you supplied the external energy, to "create the power" by utilizing the difference in temperatures, you will eventually lose since what you have is essentially a heat engine and TD. That tells you that the maximal efficiency of such a heat engine is expressed as (Th-Tc)/Th in which Th is the hot temperature and Tc is the cool temperature. As we can see from the expression, the efficiency is less than 100% to run a heat engine. Eventually, the energy is lost during the process along the time. Therefore, nature won't let me generate something with nothing.

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