p-v diagrams and processes c ontents: basic concept example whiteboards

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