2nd law of ther

用戶98670

2010-03-01 9:41 am

1)The figure is a
圖片參考：http://session.masteringphysics.com/render?tex=%5Crm+K
. Process ab is at constant volume, process ac at constant pressure.

圖片參考：http://imgcld.yimg.com/8/n/HA00021001/o/701003010013213873414420.jpg

a)Is the path of the cycle carried out clockwise or counterclockwise?

b)What is the efficiency of this engine?

圖片參考：http://session.masteringphysics.com/render?tex=e
=__%

2)An ideal gas expands isothermally (
圖片參考：http://session.masteringphysics.com/render?tex=%5Crm+atm
.
What is the entropy change for this process?

圖片參考：http://session.masteringphysics.com/render?tex=%5CDelta+S
=9.3J/K
PLEASE EXPLAIN IN details

更新1:

the 1st problem i have solved... please help me the 2nd one

回答 (1)

Prof. Physics

2010-03-03 6:17 pm

✔ 最佳答案

2. There maybe some difference between my answer and your model answer since the value of atm is not the same.

By Equation of states, pV = nRT

(7.3 X 1.013 X 10^5)(2.50 X 10^-3) = nR(410)

nR = 4.51

For the isothermal process, by Boyle's law,

P1V1 = P2V2

7.3V1 = 1V2

V2/V1 = 7.3

Entropy change,
圖片參考：http://session.masteringphysics.com/render?tex=%5CDelta+S
= S dQ/T

= 1/T S nRT / V dV

= nR S 1/V dV

= nR ln(V2 / V1)

= (4.51) ln7.3

= 8.96 J/K

There is some difference, because the value of 1 atm in your model is different from mine. Anyway, the solution above is valid.

參考: Physics king

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