Activity 1.2.4 Circuit Calculations
Introduction
Regardless of circuit complexity, circuit designers as well as users need to be able to
apply basic electrical theories to circuits in order to verify safe operation and
troubleshoot unexpected circuit failure. In this activity you will gain experience applying
Ohm’s law and Kirchhoff’s voltage and current laws to circuits in order to gain
understanding of circuit requirements and relationships between voltage, current, and
resistance.
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Equipment
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Engineering notebook
Pencil
Calculator
Procedure
1.
For each of the resistors shown below, use Ohm’s law to calculate the unknown
quantity. Be sure to put your answer in proper engineering notation and use the correct
units.
3.5/470=7.4 milliamps
3.5/15.5=.226 ohms
22x1.4=30.8 v
2.
For each of the circuits shown below, calculate the value for RT. Be sure to put
your answer in proper engineering notation and use the correct units.
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Principles of Engineering Activity 1.2.4 Circuit Calculations – Page 1
820+150+1200= 2170 ohms
5.6+680+8200=8885.6 ohms
3.
Using the laws of circuit theory, solve for RT, IT, V1, V2, and V3. Be sure to put
your answer in proper engineering notation and use the correct units.
RT=270+470+1200
V/R=I
RT=1940 ohms
9/1940=4.63 milliamps
V1= 4.63mAx 470
V2=4.63mAx1200 V3=4.63x270
V1=2.17v
V2=5.56v
V3=1.25v
Using the data from problem 3, verify your results using Kirchhoff’s voltage law.
all the added voltage equals the total voltage
4.
Using the laws of circuit theory, solve for RT, IT, I1, I2, and I3. Be sure to put your
answer in proper engineering notation and use the correct units.
RT=8200+6800+4700
IT=V/R
RT=19.7 kiloohms
I=12/19700
I=.609 kA
Using the calculated results from problem 4, verify your results using Kirchhoff’s current
law.
Conclusion Questions
1.
State two rules for the voltage and current in a series circuit.
a.
voltage stays the same
b.
total resistance is the same as the individual resistance
2.
State two rules for the voltage and current in a parallel circuit.
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Principles of Engineering Activity 1.2.4 Circuit Calculations – Page 2
a.
voltage is the same as the individual voltage
b.
sum of the currents through each path is equal to the total current
3.
If you remove a single bulb from an inexpensive string of Christmas tree lights, all
of the lights in the entire string will go off. Are the bulbs connected in series or parallel?
Explain.
They are connected in a series circuit because if part of a parallel circuit goes out it will
still work while a series circuit will stop working.
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Principles of Engineering Activity 1.2.4 Circuit Calculations – Page 3