EAS 199B Homework 7-Solution
1. An 18 ohm resistor will be used to heat the water in your fishtank. Will a 12VDC power
supply capable of delivering 1 amp be able to power this heater (resistor)? Use Ohm’s law
to show whether or not the power supply will be able to deliver the required current.
2. An 18 ohm resistor will be used to heat the water in your 1.6 inch diameter fishtank. If a
12VDC power supply is used and the water in your fishtank is 1.5 inches deep, then how
long will it take to heat the water in the tank up by 1oC? Assume that the density of water is
1000 kg/m3. 25.8 seconds
3. Assume that you need to choose a resistor to serve as a water heater for your 1.6-inch
diameter, 1.5-inch deep fishtank. If a 12VDC power supply is used and a heating rate of 2oC
per minute is required, then what size of resistor should you choose? Assume that the
density of water is 1000 kg/m3. 20.9Ω
4. Using the data supplied in the spreadsheet for R vs T for
a given thermistor, calculate the voltage input to the
arduino for the circuit shown. Plot V vs T and develop the
equation for the trendline.


10k
VOut  
VIn
10k  RThermistor 
Temperature
°C
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
Resistance
Ω
32554
25339
19872
15698
12488
10000
8059
6535
5330
4372
3605
2989
2490
2084
1753
1481
1256
1070
915.4
786
677.3
VOut
V
1.17
1.41
1.67
1.95
2.22
2.50
2.77
3.02
3.26
3.48
3.68
3.85
4.00
4.14
4.25
4.36
4.44
4.52
4.58
4.64
4.68
5.00
y = -3.05E-04x2 + 6.67E-02x + 1.07E+00
R² = 9.99E-01
4.50
4.00
Voltage V
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
0
20
40
60
80
100
Temperature °C
5. Develop a circuit diagram for your fish tank project. Show all components schematically.
See website for lists of common symbols, or use your search engine to locate them. Do not
make up your own. Label components as appropriate.
Circuit Diagram Here