First law of thermodynamics: Difference between revisions
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<onlyinclude>The '''first law of thermodynamics''' states that the change in [[internal energy]] of a system (Δ''U'') is equal to the [[work]] done by or to the [[system]] (''W'') and the [[heat]] that flows in or out of it (''Q'').</onlyinclude> | <onlyinclude>The '''first law of thermodynamics''' states that the change in [[internal energy]] of a system (Δ''U'') is equal to the [[work]] done by or to the [[system]] (''W'') and the [[heat]] that flows in or out of it (''Q'').</onlyinclude> | ||
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Δ''U'' = ''W'' + ''Q'' | Δ''U'' = ''W'' + ''Q'' | ||
This means that if energy is input to a system by doing work <m>W</m> on it, then it will get hotter. If the system is to stay the same temperature, then you must remove heat from the system - <m>Q</m>. | This means that if [[energy]] is input to a system by doing work <m>W</m> on it, then it will get hotter. If the system is to stay the same [[temperature]], then you must remove heat from the system - <m>Q</m>. | ||
The first law of [[thermodynamics]] is a generalization of the [[law of conservation of energy]], which states that energy can neither be created nor destroyed. | The first law of [[thermodynamics]] is a generalization of the [[law of conservation of energy]], which states that energy can neither be created nor destroyed. | ||
This is a particularly important law when discussing [[heat engine]]s (like car engines), because it helps to understand that heat must go somewhere - the basis for [[cogeneration]]. As an engine creates [[heat]], if the heat is not vented, the engine will become hotter and hotter, which will eventually lead to melting. Therefore, because it is impossible to achieve 100% efficiency (see [[carnot efficiency]]), heat must be vented. This can either be treated as waste heat, or used for [[cogeneration]], which is applying the waste heat to another cause, like heating a car, or heating houses. | This is a particularly important law when discussing [[heat engine]]s (like car engines), because it helps to understand that heat must go somewhere - the basis for [[cogeneration]]. As an engine creates [[heat]], if the heat is not vented, the engine will become hotter and hotter, which will eventually lead to melting. Therefore, because it is impossible to achieve 100% [[efficiency]] (see [[carnot efficiency]]), heat must be vented. This can either be treated as [[waste heat]], or used for [[cogeneration]], which is applying the waste heat to another cause, like heating a car, or heating houses. | ||
To learn more about the first law of thermodynamics, please check out [http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/firlaw.html#c1 hyperphysics]. | To learn more about the first law of thermodynamics, please check out [http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/firlaw.html#c1 hyperphysics]. | ||
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Revision as of 20:08, 3 September 2015
The first law of thermodynamics states that the change in internal energy of a system (ΔU) is equal to the work done by or to the system (W) and the heat that flows in or out of it (Q).
The equation for this relationship is: ΔU = W + Q
This means that if energy is input to a system by doing work on it, then it will get hotter. If the system is to stay the same temperature, then you must remove heat from the system -
.
The first law of thermodynamics is a generalization of the law of conservation of energy, which states that energy can neither be created nor destroyed.
This is a particularly important law when discussing heat engines (like car engines), because it helps to understand that heat must go somewhere - the basis for cogeneration. As an engine creates heat, if the heat is not vented, the engine will become hotter and hotter, which will eventually lead to melting. Therefore, because it is impossible to achieve 100% efficiency (see carnot efficiency), heat must be vented. This can either be treated as waste heat, or used for cogeneration, which is applying the waste heat to another cause, like heating a car, or heating houses.
To learn more about the first law of thermodynamics, please check out hyperphysics.