ENGR 121
Section______ Instructor:_____________ Name: ____________________________
Form#: 11
February 27, 2012
Allowed materials include calculator (without wireless capability), pencil or pen.
Honor Statement: On my honor, I promise that I have not received any outside assistance on this exam (I didn’t look at another
student’s paper, I didn’t view any unauthorized written materials, I didn’t talk or listen to another student, . . .).
___________________________________________signature
4 1 2 1
11
12
13
14
01
02
03
04
H11
H12
H13
H14
001
002
003
004
8-9:50 TR
2-3:50 TR
2-3:50 MW
10-11:50 MW
8-9:50 MW
10-11:50 MW
10-11:50 TR
12-1:50 TR
Hall
Cronk
Swanbom
Watson
Barker
Crittenden
Watson
Barker
also fill in CWID, name and course (121) . . . don’t forget to black in bubbles
you must show your work on problems that require calculations to receive credit
Problem 1
(3 points) The layer of material between the nickel and the glass slide on your RTDs was . . .
a. PVC
b. tungsten
c. photoresist
d. silver
e. chromium
Problem 2
(3 points) The class notes listed the advantages and disadvantages of several temperature
sensors. The sensor that gives the “most linear” output as temperature increases is . . .
a.
b.
c.
d.
thermocouple
RTD
thermistor
I.C. sensor (integrated circuit sensor)
Problem 3
(3 points) The current salinity of a fish tank system is 0.20 wt% NaCl which happens to be above
the UCL. If the setpoint is 0.10 wt% NaCl and the gain is 0.6, then the target concentration for
your fish tank system would be . . .
a.
b.
c.
d.
e.
0.04 wt% NaCl
0.06 wt% NaCl
0.10 wt% NaCl
0.14 wt% NaCl
0.16 wt% NaCl
Problem 4
(3 points) What programming command do you use to switch the Arduino from using a 5V
analog-to-digital conversion reference voltage to a 1.1V analog-to-digital conversion reference
voltage?
a.
b.
c.
d.
e.
f.
analogReference(DEFAULT);
analogReference(BULLDOGS);
analogReference(INTERNAL);
analogReference(EXTERNAL);
analogReference(1.1);
analogReference(5,1.1);
Problem 5
(3 points) The substance degraded by UV light that is used in the process of fabricating RTDs is
called . . .
a.
b.
c.
d.
e.
photoresist
nitric acid
photolithography
developer
UVdubeedo
Problem 6
(3 points) Which of the following is a correct representation of the units of resistivity (a material
property)?
a. Ω
b. volt ∙ Ω
c. Ω ∙ m
d.
Ω
m2
e. Ω ∙ A
Problem 7
(3 points) Where does the power come from that is used to energize the coils on your relays on
the fish tank system (if you hook it up as shown in the notes)?
a.
b.
c.
d.
e.
directly from an Arduino pin
from the 5V voltage regulator on the Arduino
from a 12V power supply plugged into an electrical outlet
from an analog input pin on the Arduino
from the solenoid valve
Problem 8
(3 points) Temperature readings from the RTD were sensed by the Arduino using . . .
a.
b.
c.
d.
e.
a digital input
a digital output
an analog input
an analog output
a transistor circuit
Problem 9
(3 points) The proportionality constant for computing the target concentration (C2 was the
target concentration in the notes) of the water in the fish tank is…
a.
b.
c.
d.
Oscillation
Gain
3s
Weight % Salt
Problem 10
(3 points) Each ENGR 121 student group performed 4 of the 6 steps required to fabricate an
RTD sensor using the Ultraviolet Photolithography method. Which of the following 5 diagrams
represents the RTD after the developing step has been completed ?
a. f
b. A
c.
D
d. D
e. D
Problem 11
(5 points) A student has 20 kg of a salt water solution with an unknown concentration of salt.
After adding 5 kg of DI water, she measures the concentration of the final solution to be 2% NaCl
by mass. The percentage by mass of salt in the initial solution must be:
a.
b.
c.
d.
e.
f.
g.
0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
3.0%
Problem 12
(5 points) After you finish this final exam, you would like to have a hot bath. You know that your
bathtub holds 180 liters of water. The cold water line to your apartment will supply water at a
temperature of 15° C, and the hot water heater will supply water at a temperature of 60° C. If
you want the bath water to have a temperature of 40 ° C, then how much hot water and how
much cold water will you need to draw into the tub?
a.
b.
c.
d.
e.
f.
g.
h.
i.
40 L hot water; 140 L cold water
50 L hot water; 130 L cold water
60 L hot water; 120 L cold water
70 L hot water; 110 L cold water
80 L hot water; 100 L cold water
90 L hot water; 90 L cold water
100 L hot water; 80 L cold water
110L hot water; 70 L cold water
120 L hot water; 60 L cold water
Problem 13
(5 points) Your team’s best RTD has a value of only 60.5 ohms at room temperature. Assuming
that you use the Arduino’s internal analog reference voltage (1.1V) for the RTD circuit, then the
maximum value you can use for the lower resistor (RLower) in your circuit would be:
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
10 W
11 W
12 W
13 W
14 W
15 W
16 W
17 W
18 W
19 W
Problem 14
(5 points) A cow has an average specific heat (Cp) of 3550 J / kg-°C. Normally, the cow has an
average body temperature of 39 °C. Suppose the cow becomes overheated during a hot summer
day, and his body temperature rises to 43 ° C. The cow has a body mass of 800 kg. To bring the
cow’s temperature back to his normal value, the farmer decides to submerse the cow in a bath
of water which is at room temperature (22 ° C). Assume that the cow’s physiological (metabolic)
processes are not contributing to the raising or lowering of his body temperature. The amount
of water required to reduce the cow’s temperature back to 39 ° C is closest to…
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
20 kg
40 kg
60 kg
80 kg
100 kg
120 kg
140 kg
160 kg
180 kg
200 kg
Problem 15
(5 points) You are back at the milk plant and it has become apparent that you need to expand
your product line to include chocolate milk. You have been asked to create 100 liters per hour of
a low-fat chocolate milk that has a 5% fat content. You decide to use skim milk with 0.5% fat and
5% carbohydrates and mix it with a low-fat cocoa that contains 10% fat and 50% carbohydrates.
The density of the resulting chocolate milk will be 1.05kg/L. The rate of skim milk required will
be closest to…
a.
b.
c.
d.
e.
f.
40 kg/hr
45 kg/hr
50 kg/hr
55 kg/hr
60 kg/hr
65 kg/hr
Problem 16
(5 points) You are asked to design a 50 Ohm resistor on a glass slide that is 1 inch x 1 inch. You
have been told to use the following pattern and now you need to select the appropriate metal to
use with your design. You will be using a process that creates a wire with a rectangular cross
section with a thickness of 0.3 microns (mm) and a width of 0.4 mm. Select the metal from the
table below that results in an RTD whose resistance is closest to the 50 Ohm target value.
6.35 mm
19.05 mm
a.
b.
c.
d.
e.
f.
Aluminum
Copper
Iron
Lead
Mercury
Tungsten
METAL
Aluminum
Copper
Iron
Lead
Mercury
Tungsten
RESISTIVITY (ohm*meters)
2.82 x 10-8
1.7 x 10-8
1.0 x 10-7
2.2 x 10-7
9.8 x 10-7
5.6 x 10-8
Problem 17
(5 points) You are heating a 10 gallon freshwater fish tank with a store bought fish tank heater.
You want to heat the water over the next 24 hours from room temperature (20 degrees Celsius)
to 26 degrees Celsius. If you are using a 110 Volt heater, the current required will be closest to:
Assume:
a.
b.
c.
d.
e.
f.
no heat loss from the tank
0.026 A
0.1 A
0.5 A
0.6 A
1.0 A
2.4 A
Problem 18
(5 points) You just made a nice cup (0.237 Liters) of green tea, but it is too hot to drink. You
measured the temperature and it was 70 degrees Celsius. You prefer to drink your tea at 60
degrees Celsius. You plan to cool your tea by submerging two-thirds (2/3) of a number of
stainless steel spoons in the tea. These spoons are at room temperature (20 degrees Celsius).
Only the submerged portion of the spoons will change temperature. How many of these
spoons will be required to accomplish this?
Assume:
a.
b.
c.
d.
e.
f.
Cp for tea = 4185 J/kg-°C
Cp for stainless steel = 502 J/kg- °C
density of tea= 1000 kg/m3
no heat loss from the cup
mass of entire spoon = 75 grams
2 spoons
4 spoons
6 spoons
8 spoons
10 spoons
12 spoons
Problem 19
(5 points) An intravenous (I.V.) bag containing 1000 mL of a salt and water solution with a weight
% of 0.09% salt will soon be infused into a patient. The physician in charge of the patient is
displeased with the current salt solution of 0.09% weight salt and would like to lower the salt
concentration to 0.07% because the patient requires a lower sodium intake. The physician wants
to add deionized water to the salt solution to lower the overall salt concentration to 0.07%. The
amount of DI water that must be added to the original solution is closest to…
a.
b.
c.
d.
e.
50 mL
150 mL
280 mL
420 mL
550 mL
Problem 20
(5 points) How many gallons of water would you need to mix with 20.5 grams of salt to create a
concentration of 0.08% weight percent NaCl?
a.
b.
c.
d.
e.
5.5 gal
6.8 gal
7.2 gal
9.4 gal
10.3 gal
Problem 21
(5 points) The picture to the right shows a chlorine generator for use with salt-water pools. Its
job is to electrolyze the salty water to produce chlorine gas (which stays in solution in the
water). The model shown here produces up to 1.40 pounds of chlorine per day. If the chlorine
generator runs all the time and produces 1.40 pounds of chlorine per day, the electrical current
required between its electrodes is closest to…
a.
b.
c.
d.
e.
f.
g.
h.
i.
1.895A
5.918A
8.519A
15.89A
18.59A
19.85A
51.98A
81.95A
98.15A
Photo courtesy of Pentair Water
Problem 22
(5 points) You are trying to design a nickel film RTD similar to the ones we built in class. The
target resistance between the solder pads is 24Ω. The nickel film has a thickness of 0.2
micrometers, and a resistivity of 6.85x10-8 Ω∙m. The best estimate for the required width of the
lines is…
(NOTE: All vertical distances are either 2.5 mm or 5 mm and all horizontal distances are either
1.9 or 3.8 mm.)
a.
b.
c.
d.
e.
f.
0.192mm
0.257mm
0.395mm
0.539mm
0.753mm
0.935mm
Problem 23
(5 points) Dr. Hall loves coffee. He loves it the best when it has a temperature of 93°C. He wants to
make a resistance heater (similar to the one we used in the fish tank project) using a 12V car battery
as the energy source that will heat his 12oz. (355mL) coffee from 86°C to 93°C in exactly 5 seconds.
Assuming his coffee has the same properties as water, the resistance that he needs for his resistance
heater is closest to . . .
a.
b.
c.
d.
e.
f.
0.02936 Ω
0.03692 Ω
0.05923 Ω
0.06932 Ω
0.07236 Ω
0.09263 Ω
Problem 24
(5 points) Alligators are cold-blooded, meaning they assume the temperature of their surroundings.
Suppose a 340 kg alligator whose tissue has a specific heat of 3300 J/kg°C sits for a long time in the
sun, until his average temperature reaches 50°C. Feeling lucky, Dr. Cronk (Cp = 3470 J/kg°C; mass =
100 kg; Temperature = 37°C) runs up to the alligator to pull his tail. Not being so lucky, he gets
snatched by the alligator and killed (may he rest in peace). The alligator then takes Dr. Cronk’s
lifeless corpse and slips into a perfectly insulated 800 gallon pond nearby. If the initial temperature
of the pond was 20°C, then the final temperature of the alligator-Dr. Cronk-pond system after a long
period of time is closest to:
to . . .
(Assume the alligator does not generate thermal energy over time, i.e. exothermic chemical reactions are not taking place within the alligator.)
a.
b.
c.
d.
e.
f.
g.
h.
20.008 °C
20.08 °C
20.80 °C
22.80 °C
24.08 °C
26.08 °C
28.80 °C
30.80 °C
1 coulomb = 6.28(10)18 electrons
Avogadro’s Number: 6.022(10)23
Density of water at 4°C (maximum density) = 1 g/mL= 1g/cm3 = 1000 kg/m3 = 8.33 lbs/gal
Specific Heat of Water: 𝐶𝑃 = 4180
𝐽
𝑘𝑔∙𝐶
1L = 0.001m3 = 1.0567quarts = 0.264gal = 61.02in3
1 pound = 453.592 grams
1 gal = 0.1337 ft3
1 inch = 25.4 mm
Conductivity Sensor Reactions:
2𝐶𝑙 −𝑎𝑞
𝐶𝑙2 (𝑔) + 2𝑒 − and
2𝐻20(𝑙) + 2𝑒 −
−
𝐻2 (𝑔) + 2𝑂𝐻(𝑎𝑞)
Atomic Weights:
Na = 23.0 g/mol, Cl = 35.5 g/mol, C = 12.0 g/mol, H = 1.0 g/mol, O = 16.0 g/mol
𝜌∙𝐿
𝑅=
𝐴
𝑅2 − 𝑅1
𝛼=
𝑅1 𝑇2 − 𝑇1
Volume of Cylinder =
𝜋 ∙ 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 2
4
∙ ℎ𝑒𝑖𝑔ℎ𝑡
𝑉 ∙ 𝐼 ∙ 𝑡 = 𝜌 ∙ 𝑉𝑜𝑙 ∙ 𝐶𝑝 ∙ ∆𝑇