PhysicsLAB AP Free Response Question
2009 B4 Form B

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The cylinder shown below has an open top, and gas is held inside it by a piston of mass m and area A. The gas is insulated from its surroundings and is initially in equilibrium at volume Vi . Express all algebraic answers in terms of the given quantities and fundamental constants.
 (a) Determine the absolute pressure Pi of the gas at equilibrium.

The gas is heated by a circuit that contains three resistors, each of known resistance R0, connected in parallel to a power source of emf . The piston is held fixed so that the gas remains at constant volume while being heated for a period of time t.
 (b) Determine the resistance of the circuit.

 (c) Calculate the change in internal energy of the gas.

After the time t, the circuit is disconnected. The piston is then released and the gas is allowed to expand adiabatically until it reaches volume Vf.
(d) Indicate below whether the temperature increases, decreases, or remains the same during this process. Justify your answer.

_____ Increases
_____ Decreases
_____ Remains the same

(e) The gas is then compressed isothermally to its original pressure and volume. On the axes below, draw a PV diagram for the complete cycle described in this question, labeling Vi and Vf on the volume axis.

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