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Re: [Phys-l] PV question

Perhaps if I concede that I defined the process in question too narrowly
(after all the ascii diagram shows that pressure doubles while the volume halves, apparently) then John will not demur if I deny that a pressure changing process is isobaric, nor suppose a volume changing process is isochoric? :-)

Brian W

John Mallinckrodt wrote:
Biran Whatcott wrote:

If one specifies a straight line on such a PV graph, then the curve
describing the pressure volume and temperature change during its
compression will necessarily cut some isotherm (actually many of them)

Not so. Not in the case of an isobaric or isochoric process or, for that matter, many other processes. Consider, for instance, any process for which P(V) = P_o + C (V - V_o) with C a positive constant. In fact, depending on starting and ending volumes, many processes with negative C also satisfy the requirement. All of these processes can be carried out reversibly.

The implication (for me) is that this straight line is not a description
of a reversible adiabatic. process.

That's *certainly* true, but you don't need to and, in fact, can't deduce that result from any of the foregoing observations. A reversible adiabatic process is described by a curved line on a PV graph, period.

John Mallinckrodt
Cal Poly Pomona
Forum for Physics Educators