Physics 110 Problems - My Solutions
Dr. Hulan E. Jack Jr.
Chapter 11 E9 Griffith, W. Thomas; The physics of everyday phenomena: a conceptual introduction for physics;4th
Edition ISBN 0-07-250977-5
THE PROBLEM STATEMENT
Ch11 E9 A heat pump takes in 300 J of heat from a low-temperature reservoir in each cycle and
uses 150 J of work per cycle to move the heat to a higher-temperature reservoir. How much heat
is released to the higher-temperature reservoir in each cycle?
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Physics 110 Problems - My Solutions
Dr. Hulan E. Jack Jr.
Basic Solution (Minimum Expected from the student)
Ch11 E9 A heat pump takes in 300 J of heat from a low-temperature reservoir in each cycle and
uses 150 J of work per cycle to move the heat to a higher-temperature reservoir. How much heat
is released to the higher-temperature reservoir in each cycle?
The 1st Law of Thermodynamics Cycle QH –QC = Work , where
QH is the released from the hot (high temperature) reservoir ,
QC is the heat released into the cold (low temperature) reservoir,
and
Work is the work done by the system on the environment.
For the heat engine these value are positive direction of the flow.
For the heat pump the flow is reversed,
QH is now released into the hot reservoir so it is negative ,
QC is now released from the cold reservoir so it is negative
Work is now done on the system by the environment, so it is negative.
(FOLLOW THE COLORS ABOVE x y z )
So
QH –QC = Work , QH = Work +QC; -150 J + (-300J) = -150-300 - -450J.
THE QUICK COPOUT AND SAVE YOUR SANITY
The absolute value QH , |QH|, the heat released, must equal absolute value
of QC, |QC| , the heat absorbed (taken in) + the work done on the heat pump
, |Work|.
|QH| = |QC| + |Work | = 300J + 150 J = 450J.
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