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# LPH 105 W15 15:1-4

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## Richard Datwyler

on 14 July 2016

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#### Transcript of LPH 105 W15 15:1-4

Thermodynamics
First law
Heat engines
Efficiency
table
First law
An ideal gas expands isothermally, performing 4.3 X 10 ^3 J of work in the process. Calculate
The change in internal energy of the gas
the heat absorbed during this expansion.

The pressure in an ideal gas is cut in half slowly, while being kept in a container with rigid walls. In the process, 465 J of heat left the gas
How much work was done during this process
What was the change in internal energy of the gas during this process?

0
0 -465 J
8.5 Moles of an ideal monatomic gas expand adiabatically, performing 8300 J of work in the process. What is the change in temperature of the gas during this expansion?
-78
Consider the following two-step process. Heat is allowed to flow out of an ideal gas at constant volume so that its pressure drops from 2.2 atm to 1.4 atm. Then the gas expands at constant pressure, from a volume of 5.9 L to 9.27 L, where the temperature reaches its original value.
Draw this process on a PV graph
What is the total work done by the gas in the process?
What is the total heat flow into or out of the gas?
477.9 J
477.9 J
A certain power plant puts out 580 MW of electric power. Estimate the heat discharged per second, assuming the plant has an efficiency of 32%.
1230 MJ
The following is an engine, Let P1=P2 = 425000 Pa, V1=.002 m^3 and V2 =.008
fill out engine table
What is the total work done per cycle?

How much heat was taken in?
exhausted?

what is the efficiency of the engine?
2550 6375 3825 J
0 -3825 -3825 J
-1178.35 -1178.35 0 J
1371.65 J
6375 J
5003.35 J
21.5 %
The following is an engine, Let P1=P2 = 425000 Pa, V1=.002 m^3 and V2 =.008
Run same problem, but go this way.

What is the total work done per cycle?

How much heat was taken in?
exhausted?

what is the efficiency of the engine?
fill out engine table
1178.35 1178.35 0 J
-637.5 -1593.75 -956.25 J
0 956.25 956.25 J
540.85 540.85 0 J
540.85
2134.6 J
25.3%
"Are the four processes with specific constant factors only for the first law of thermodynamics? "
"Can you please clarify how pressure can remain constant (isobaric) if volume changes? I thought they were inversely proportionately related."
"Can you go over how to solve the area under the graph problems? That would be dandy."
"Obviously number 4 on the quiz. "
425000
.002
.008
1
2
3
4300 J
425000
.002
.008
3
2
1
1371.65 1371.65 0 J
How much work is done in an isobaric process at a constant 101 kPa if the volume goes from 0.001 m^3 to 0.005 m^3? (answer should look like '215 J')
"I don't understand the concept of transforming KE into internal energy. Is it just that it increased the temperature of the object?"
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