. Applied thermodynamics for engineers. cific value of n and for definite ratios F -^ y we maytabulate successive values of logjo and of p. Such tables for various values of nare commonly used. In employing them, the final pressure is found in terms ofthe initial pressure for various ratios of final to initial volume. 119. Representation of Internal Energy. In Fig. 35, let An represent an adiabatic. During expansion from A to a, the external work done isAabc, wliiclij from the law of the adiabatic, isequal to the expenditure of internal energy. Ifexpansion is continued indefinitely, the adiaba
. Applied thermodynamics for engineers. cific value of n and for definite ratios F -^ y we maytabulate successive values of logjo and of p. Such tables for various values of nare commonly used. In employing them, the final pressure is found in terms ofthe initial pressure for various ratios of final to initial volume. 119. Representation of Internal Energy. In Fig. 35, let An represent an adiabatic. During expansion from A to a, the external work done isAabc, wliiclij from the law of the adiabatic, isequal to the expenditure of internal energy. Ifexpansion is continued indefinitely, the adiabaticAn gradually approaches the axis OV, the areabelow it continually representing expenditure ofinternal energy, until with infinite expansion Anand OF coincide. The internal energy is then ex-hausted. The total internal energy of a substancemay therefore be represented by the area betweenthe adiabatic through its state, indefinitely prolonged to the right, and the horizontal axis. Eepresenting this quantity by E, then from Art. Ill, E. Fig. 35. Art. 119. —Repre-sentation of InternalEnergy. = i pdv = -^— where v is the initial volume, p the initial pressure, and y the adiabaticexponent. This is a finite and commensurable quantity. 120. Representation by Isodynamic Lines. A defect of the precedingrepresentation is that the areas cannot be included on a finite diagram. GRAPHICAL REPRESENTATIONS 63 In rig. S6j consider the path AB. Let -BC be an adiabatic and AC an-isodynamie. It is required to find the change of internal energy betweenA and B. The external work done during adi-abatic expansion from Bio C is equal to BCcb;and this is equal to the change of internal en-ergy between B and C. But the internal energyis the same at C as at A, because AC is anisodynamic. Consequently, the change of in-ternal energy between ^ and B is representedby the area BCcb; or, generally, by the areaincluded between the adiabatic through the finalstate, extended to its intersection with the iso
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