P-V Diagrams and processesContents:• Basic Concept• Example• Whiteboards
P-V diagrams
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The axesChange volume?Change pressure?
Volume
Pres
sure
Isobaric Expansion (+W)
Isobaric Compression (-W)
Iso = samebaric = pressure
P-V diagrams
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Volume
Pres
sure
Isochoric = same volume(closed container)how does it happen?
Adiabatic (no heat flow) processes
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Volume
Pres
sure
Adiabatic expansion: (Q = 0)Work is done by the gas (+W)No heat flows in: Q = U + W0 = U + W, U = -WInternal energy (T) drops
ExamplesAir rocketsCold side of fridgeUniverseDemo - cloud
Adiabatic (no heat flow) processes
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Volume
Pres
sure
Adiabatic compression: (Q = 0)Work is done on the gas (-W)No heat flows in: Q = U + W0 = U + W, U = -(-W)Internal energy (T) rises
ExamplesBike pump/dieselsHot side of fridgeCompressorsDemo – plunger/Murray Frig
Isothermal (constant temperature) processes
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Volume
Pres
sure
Isothermal expansion: (T = 0)Work is done by the gas (+W)Internal energy is constant (U = 0)Q = U + W = W Heat turns to work (slowly)
Isothermal (constant temperature) processes
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Volume
Pres
sure
Isothermal compression: (T = 0)Work is done on the gas (-W)Internal energy is constant (U = 0)Q = U + W = W Work turns to heat (slowly)
What’s goin’ on here?
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Volume
Pres
sure
isobaric expansionheat flows in, temp increases
What’s goin’ on here?
TOC
Volume
Pres
sure
isochoric coolingheat flows out, pressure drops
What’s goin’ on here?
TOC
Volume
Pres
sure
isochoric heating, isobaric expansion
Which process is adiabatic, which is isothermal?
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Volume
Pres
sure
In which process would the temperature drop?B is adiabatic
AB
Which process is adiabatic, which is isothermal?
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Volume
Pres
sure
In which process would the temperature increase?B is adiabatic
A
B
A complete cycle:
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Volume
Pres
sure
Complete cycle - where is work done?Is more work done by gas or on the gas?
A
B C
D