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P-V Diagrams and processesContents:• Basic Concept• Example• Whiteboards
P-V diagrams
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The axesChange volume?Change pressure?
Volume
Pre
ssur
eIsobaric Expansion (+W)
Isobaric Compression (-W)
Iso = samebaric = pressure
P-V diagrams
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Volume
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ssur
e
Isochoric = same volume(closed container)how does it happen?
Adiabatic (no heat flow) processes
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Volume
Pre
ssur
e
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
TOC
Volume
Pre
ssur
e
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
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ssur
e
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
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e
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
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ssur
e
isobaric expansionheat flows in, temp increases
What’s goin’ on here?
TOC
Volume
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ssur
e
isochoric coolingheat flows out, pressure drops
What’s goin’ on here?
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Volume
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e
isochoric heating, isobaric expansion
Which process is adiabatic, which is isothermal?
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Volume
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ssur
e
In which process would the temperature drop?B is adiabatic
A
B
Which process is adiabatic, which is isothermal?
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Volume
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ssur
e
In which process would the temperature increase?B is adiabatic
A
B
A complete cycle:
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Volume
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ssur
e
Complete cycle - where is work done?Is more work done by gas or on the gas?
A
B C
D