Squeezing a piston and its effect on temperature

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SUMMARY

When a piston is compressed, the temperature of the gas inside increases due to the work done on the gas, as indicated by the first law of thermodynamics (U=Q + W). In an insulated system, where Q=0, the internal energy U increases solely from the work W done on the gas. The confusion arises from the misapplication of Boyle's law, which assumes constant temperature; however, for an ideal gas, the relationship between pressure, volume, and temperature is governed by the ideal gas law (PV=nRT).

PREREQUISITES
  • Understanding of the first law of thermodynamics (U=Q + W)
  • Familiarity with the ideal gas law (PV=nRT)
  • Knowledge of Boyle's law and its assumptions
  • Basic concepts of thermodynamics and gas behavior
NEXT STEPS
  • Study the implications of the first law of thermodynamics in closed systems
  • Learn about the ideal gas law and its applications in thermodynamics
  • Explore the conditions under which Boyle's law applies
  • Investigate the relationship between work done on a gas and changes in temperature
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Students studying thermodynamics, physics enthusiasts, and anyone looking to understand the behavior of gases under compression.

qazxsw11111
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Homework Statement


If a piston is compressed, how is the temperature affected?


Homework Equations


U=Q + W


The Attempt at a Solution



My soln: I thought that U=k.e. = (3/2)nRT=(3/2) pV ?
Since PV is constant (P1V1=P2V2), shouldn't temperature be constant?

Answer sheet: My answer sheet says that Q=0 since piston is insulated. and U=W. Since it is compressed, work is done on the gas, increasing its U, which increases T.

Which answer is correct?
 
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Hi qazxsw11111,

qazxsw11111 said:

Homework Statement


If a piston is compressed, how is the temperature affected?


Homework Equations


U=Q + W


The Attempt at a Solution



My soln: I thought that U=k.e. = (3/2)nRT=(3/2) pV ?
Since PV is constant (P1V1=P2V2), shouldn't temperature be constant?

(P1V1=P2V2) is not always true; Boyle's law assumes that the temperature and amount of gas is kept constant.

If the amount of gas is constant, then for an ideal gas you would use:

[tex] \frac{P_1 V_1}{T_1}=\frac{P_2 V_2}{T_2}[/tex]

which follows directly from the ideal gas law.
 

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