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DC Fundamentals
Series/Parallel Resistive Circuits
Exercise 2: Voltage in a Series/Parallel Circuit
EXERCISE OBJECTIVE
Ohm’s law. You will verify your results with a multimeter.
DISCUSSION
In a series/parallel circuit, voltage across each circuit branch is distributed in proportion to the resistive
value of each branch.
In this circuit, the applied voltage equals the voltage across R1 plus the voltage across the parallel branch
(R2 or R3).
In this circuit, the voltage across R2 (VR2) equals
a. VR3.
b. VR1.
c. VA.
In this circuit, IT
R1 = IT x R1 or IR1 x R1.
We may use the value of IT for IR1 because the amount of current through any series element of the
circuit is identical to the total current of the circuit.
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DC Fundamentals
a. VA = VR3 + VBC
b. VA = VR1 + VR2
c. VA = VR1 + VR2 + VBC
PROCEDURE
฀
Locate the SERIES/PARALLEL CIRCUIT circuit block, and connect the circuit shown.
฀
Measure the value of the circuit source voltage.
VA =
Vdc (Recall Value 1)
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฀
Measure the voltage drop of R1.
VR1 =
฀
Vdc (Recall Value 2)
Measure the voltage drop of R2.
VR2 =
฀
Series/Parallel Resistive Circuits
Vdc (Recall Value 3)
Measure the voltage drop of R3.
VR3 =
Vdc (Recall Value 4)
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฀
DC Fundamentals
Based on your data recalled below, which statement properly relates the voltage drops of
your circuit?
a. The voltage drops are not related because of the series/parallel combination.
b. The voltage drop of R1 indicates a circuit problem because its value is not equal to that of
VR2 or VR3.
c. The voltage drops are correct because the sum of the series and parallel combination
voltage drops equals VA.
VA =
Vdc (Step2, Recall Value 1)
VR1 =
Vdc (Step3, Recall Value 2)
VR2 =
Vdc (Step4, Recall Value 3)
VR3 =
Vdc (Step5, Recall Value 4)
฀
To calculate the voltage drop of R1,
a. multiply either IR2 or IR3 with the value of R1.
b. subtract the sum of VR1 and VR2 from VA.
c. multiply IT by the value of R1.
฀
Place CM switch 12 in the ON position to put R4 in the circuit.
What is the relationship of the circuit voltages with resistor R4 added?
a. VA = VR1 + VRE + VR4
b. VA = VR1 + VR4
c. VR1 = VR3 and VR2 = VR4
฀
With CM 12 still in the ON position, VR4 equals
a. IR4 x R4.
b. IT x R4.
c. (IR2 + IR3) x R4.
฀
With CM 12 still in the ON position, what are the voltage drops of R2 and R3?
a. about 15 Vdc
b. about 4.45 Vdc
c. about 9.7 Vdc
฀
Make sure all CMs are cleared (turned off) before proceeding to the next section.
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Series/Parallel Resistive Circuits
CONCLUSION
•
In a series/parallel circuit, the sum of the branch voltage drops equals the source voltage of the
circuit.
•
•
In a series/parallel circuit, the voltage drops across each resistor of a parallel element are equal.
REVIEW QUESTIONS
1.
a.
b.
c.
d.
E = I/R
E = IR
E = R/I
E = E/RI
2. In a series/parallel circuit consisting of three equal 5 k: resistors, the voltage drop is
a. greatest across the parallel branch.
b. greatest across the series branch resistor.
c. equal across all the branches.
d. None of the above.
3. What information do you need to calculate the voltage drop across a parallel branch of a series/
parallel circuit?
a. total circuit current (IT) and equivalent resistance (RE)
b. equivalent resistance (RE)
c. applied voltage (VA)
d. None of the above.
4. In this circuit, what would be the effect if R3 were shorted?
a. VR1 would decrease.
b. VR2 would increase.
c. VRE would increase.
d. VR1 would equal VA.
5. Locate the SERIES/ PARALLEL CIRCUIT circuit block, and connect the circuit shown above. Place
a.
b.
c.
d.
A 600: resistor was placed in the parallel branch.
A 1 k: resistor was placed in parallel with R1.
A 2.7 k: resistor was placed in parallel with R2.
A 4.7 k: resistor was placed in parallel with R3.
NOTE: Make sure all CMs are cleared (turned off) before proceeding to the next section.
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