09_thermodynamicsIII_s11

# 09_thermodynamicsIII_s11 - Page 1 Entropy and Particles in...

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Entropy and Particles in a box It would take work to push all the molecules back to the left side

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Heat Engines Heat engines take heat from a hot reservoir and does work and expels heat to the cold reservoir Note that the Frst law says - Q 1 =W+Q 2 The 2nd law tells us the amount of work we can get from a temperature difference EfFciency = (work output)/(energy in)
Carnot Engine

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Real Heat Engines Real heat engines always are less efFcient than Carnot engines In all heat engines there is waste heat from the 2 nd law - Electric motors are not governed by the 2 nd – although generally the production of electricity is… In real engines there is additional waste heat The Carnot engine gives us a goal
Real Engine T 1 T 2 Q 1 Q 2 W out Q waste

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efFciency of about 25% - The efFciency may be as high as 37% at the optimum operating point. - Most internal combustion engines waste about 35% of the energy in gasoline as heat lost to the cooling system and another 35% through the exhaust. -
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## This note was uploaded on 02/28/2011 for the course PHYS 105 taught by Professor Staff during the Spring '08 term at Maryland.

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09_thermodynamicsIII_s11 - Page 1 Entropy and Particles in...

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