January 7 AP Physics. IN A gas follows the cycles shown. How much work is done?
43
January 7 AP Physics
-
Upload
savannah-flood -
Category
Documents
-
view
219 -
download
3
Transcript of January 7 AP Physics. IN A gas follows the cycles shown. How much work is done?
January 7AP Physics
IN A gas follows the
cycles shown. How much work is done?
Objective:
To study cycles in thermodynamics.
Success Criteria:
To be able to calculate the work done in a thermodynamic cycle.
Homework check
2, 5, 6, 10
PV diagram
PV diagram-holding pressure constant
PV diagram-holding volume constant
PV diagram-holding temperature constant
Work and PV diagrams (quick quiz 12.1)
Put these in order: most negative work to most positive work.
First law of Thermodynamics
ΔU = Q + W
Isobaric (pressure constant)
ΔU = Q + W
Isovolumetric (volume constant)
ΔU = Q
Isothermal (temperature constant)
ΔU = 0
Therefore
Q = W
Adiabatic (isolated system)
ΔU = W
Work in thermodynamic processes
W=FΔd
W=PAΔd
W= -PΔV
Process conditions first law
Isobaric both temp ΔU=Q+Wand volume change
Isovolumetric no work ΔV=0 so W=0so ΔU=Q
Isothermal no change ΔU=Q+W=0
in T or U so Q= - WAdiabatic no energy Q=0
transfer as so ΔU=Wheat
PV diagrams and thermodynamic processes (quick quiz 12.2)
Identify the paths
PV diagram of a cycle
Steam engine
Newcome Steam engine
Problem 4
Efficiency of an engine
Work out
Energy in
e= W
QH
Sadi Carnot1796-1832
• 1824-Reflections on the
Motive Power of Fire
• Efficiency of a heat engine
• Theoretical maximum
• Began the understanding that became the second law of thermodynamics.– entropy
Carnot cycle
Carnot cycle
The Carnot Engine
Carnot Engine
No real engine operating between two energy reservoirs can be more efficient than a Carnot engine operating between the same two reservoirs.
ec= TH-TC
TH
Three engines operate between reservoirs separated in temperature by 300 K. The reservoir temperatures are:
a) Th=1000 K Tc=700 K
b) Th=800 K Tc=500 K
c) Th=600 K Tc=300 K
Rank the engines in order of their theoretical maximum efficiency.
Second Law of Thermodynamics
No heat engine operating in a cycle can absorb energy from a reservoir and use it entirely for the performance of an equal amount of work.
You can’t have a totally efficient engine.
In any closed system, entropy always increases.
Entropy
Out:
Which of these processes are isothermal, isovolumetric, or adiabatic:
a) A tire being rapidly inflated
b) A tire expanding gradually at a constant temperature
c) A steel tank of gas being heated
