Page 66 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

mass of gas is inversely proportional to the pressure P of the gas, i.e. P  1/V (as shown

in Fig. 2.4.2-1), or P x V = constant if temperature remains constant.

P

P  1/V

1/V

Figure 2.4.2-1 Graph P  1/V

If a gas changes from state 1 to state 2 during an isothermal process, then

P1 V1 = P2 V2 = constant (2.9)

If the process is represented on a graph having axes of pressure P and volume V, the
results will be as shown in Fig. 2.4.2-2. The curve is known as a rectangular hyperbola,

having the mathematical equation xy = constant.

P

P1 1

PV = constant
P2 2

3

P3

V1 V2 V3 V

Figure 2.4.2-2 P-V graph for constant temperature
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