Download Write-up for Thermodynamics and Carnot Engine Laboratory Exercise

Your Name: _____________________________1
Name of Other Students in Group: _____________________________________
_________________________________________________________________
Lab #3
HNRT 228 Section 003 Laboratory with Mr. Lee
Heat Energy, Thermodynamics and the Carnot Cycle
Open the software for this laboratory experiment by running the
program called Exploration of Physics from your desktop.
You will find this experiment under the "heat" tab of the program's menu.
Please remember to answer all questions in complete sentences with
necessary graphics or calculations as requested.
The 1st Law of Thermodynamics and Energy Conversion
This experiment allows you to explore the relationship between
mechanical energy and heat. The falling weight drives a paddle which
stirs the water in a thermally insulated bucket. The stirring raises the
temperature of the water by a measurable amount, converting
gravitational potential energy into heat.
You will be performing the experiment several times, varying the
parameters each time. Be sure to record the water mass, initial water
temperature, hanging mass height and gravity each time.
Energy Varying Height and Mass
Perform the experiment first starting with 2 kilograms for the hanging
mass. Then change only the hanging mass, 2 kilograms greater each time,
until you get to 10 kilograms. Fill in your data table below:
Water
Mass
Initial
Temp.
Hanging
Mass
Height
Gravity
Final
Temp.
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1. As the hanging block mass increases how is the final temperature of
the water changing? Explain what is happening.
2. As you increase block mass, what is happening to the potential energy
of the block? Explain.
Now explore the changes that occur due to changes in the height.
Changing only the height, fill in the data table for this experiment.
Water
Mass
Initial
Temp.
Hanging
Mass
Height
Gravity
Final
Temp.
3. As the block height increases how is the final temperature of the
water changing? Explain what is happening.
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Name of Other Students in Group: _____________________________________
_________________________________________________________________
4. As you increase block height, what is happening to the potential energy
of the block? Explain.
Now explore the changes that occur due to changes in the water mass.
Changing only the water mass, fill in the data table for this experiment.
Water
Mass
Initial
Temp.
Hanging
Mass
Height
Gravity
Final
Temp.
5. As you increase water mass, does it take more or less energy to raise
the water to a given temperature? Explain what is happening.
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Name of Other Students in Group: _____________________________________
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Now explore the changes that occur due to changes in the initial water
temperature. Changing only the initial water temperature, fill in the data
table for this experiment.
Water
Mass
Initial
Temp.
Hanging
Mass
Height
Gravity
Final
Temp.
6. As you increase the initial water temperature, what happens to the
energy in the system? Explain.
7. How does the increasing initial water temperature affect the final
temperature? Explain.
Your Name: _____________________________5
Name of Other Students in Group: _____________________________________
_________________________________________________________________
8. What conclusions can you draw from the experiments conducted in this
laboratory exercise, regarding heat, conversion of energy and the
conditions of the experiment?
Experiment #2 – Carnot Cycle
You will find this experiment under the "heat" tab of the program's menu.
After clicking the Carnot Cycle link within the Heat tab menu you will get
to the experimental setup.
This experiment shows a Carnot cycle in action. You can choose the
values of pressure and volume between which the cycle will operate, and a
mono-atomic ideal gas in cylinder fitted with a piston is then taken
clockwise around the cycle. A table shows the heat absorbed by the gas,
the change in internal energy of the gas, and the work done by the gas
for each branch, as well as the efficiency of the cycle.
The Theory
This experiment shows a Carnot cycle in action. The engine which
performs this cycle (the Carnot Engine) represents an idealized heat
engine in which heat is converted into work by means of a cyclic process.
Taking P to be pressure and V to be volume of an ideal gas, the
relationship between P and V for an isothermal process is PV = constant.
The change in internal energy Eint of an ideal gas undergoing an
isothermal process is zero. The change in internal energy of a monoatomic ideal gas undergoing an adiabatic process from initial values PiVi to
final values PfVf is Eint = (3/2)PfVf – (3/2)PiVi.
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A Carnot engine cycle is a clockwise thermodynamic cycle made up of two
isothermal and two adiabatic processes. Equipped with the above
information as well as the First Law of Thermodynamics you have
Q = Eint + W
Q is the heat exchange from/to the gas and W is the work done by the
gas. You are then able to calculate Q, Eint, and W for each branch of
the cycle, enabling you to calculate the efficiency of the cycle, which is
equal to the total work done by the cycle divided by the total heat put
into the gas.
For the Carnot cycle, the efficiency of the cycle can more easily be found
by c =1 – Tc/Th, where Tc and Th are the coldest and hottest
temperatures of the gas during the cycle.
The Experiment and Questions
The green curves represent adiabatic processes and the red curves
represent the isothermal processes. The loop on the PV diagram is
controlled by moving the upper left and lower right corners of the cycle.
The position of the upper left is independent of the position of the lower
right. However, if one of these corners is fixed, there are limitations on
where the other corner can be.
9. Why, if one corner of the PV diagram is fixed, are there limitations on
where the other corner can be?
Note that on the PV diagram, the area enclosed by the complete cycle is
equal to the net amount of useful work extracted from the process.
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The efficiency of the cycle is calculated by taking the total work done by
the cycle and dividing it by the heat added to the cycle, that is, all the
positive values of Q added together. You can find out what Tc and Th are
for the particular cycle by clicking on the upper left and lower right
corners of the cycle.
10. Calculate the Carnot efficiency using the formula 1 – Tc/Th and
compare it to the efficiency given in the program using W/Qh. How does
your calculation compare to the efficiency provided in the program? Why
do you think there may be some difference?
11. Change the upper left and lower right bounds of the Carnot cycle to
get the largest possible efficiency. What are the values on the
boundaries that give you the largest efficiency?
12. Change the upper left and lower right bounds of the Carnot cycle to
get the smallest possible efficiency. What are the values on the
boundaries that give you the smallest efficiency?