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BASIC NEC 2023

Series-Parallel Combination Circuits & Voltage Dividers Practice Test

Free online series-parallel circuits and voltage dividers practice test. 25 basic electrical questions on combination circuit analysis, equivalent resistance, and voltage divider calculations. Good for electrician exam prep.

TOPICS COVERED

Combination Circuit Basics Series Resistance Parallel Resistance Combination Circuits Voltage Divider Basics Voltage Divider Formula

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Real circuits are often a mix of series and parallel sections combined together — these are called series-parallel (combination) circuits. Solving them means breaking the circuit into smaller series and parallel pieces, reducing each to its equivalent resistance, and working step by step. This same skill set connects directly to the voltage divider — a simple series circuit that splits a source voltage proportionally across two or more resistors.

25

Questions

38 min

Time

75%

Pass

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Series-Parallel Combination Circuits & Voltage Dividers Practice Test — Question List

Question 1: A "series-parallel" (combination) circuit is one that:

Contains some components wired in series and other components wired in parallel, combined together in the same circuit
Contains only series-wired components, with no exceptions
Contains only parallel-wired components, with no exceptions
Has no resistance anywhere in the circuit

Question 2: The general strategy for solving a combination (series-parallel) circuit is to:

Reduce each parallel section to its single equivalent resistance, then treat the resulting simplified circuit as a series circuit
Ignore the parallel sections completely
Assume all resistors have zero resistance
It cannot be solved by any systematic method

Question 3: For resistors connected in series, the total (equivalent) resistance is found by:

Simply adding all the individual resistance values together
Multiplying all the individual resistance values together
Taking the average of all the resistance values
Dividing each resistance by the number of resistors

Question 4: For exactly TWO resistors connected in parallel, the equivalent resistance formula is:

Req = (R1 x R2) / (R1 + R2)
Req = R1 + R2
Req = R1 x R2
Req = (R1 + R2) / 2

Question 5: Two resistors, 6 ohms and 3 ohms, are connected in parallel. What is their equivalent resistance?

1 ohm
2 ohms
3 ohms
9 ohms

Question 6: Three resistors, 10 ohms, 20 ohms, and 30 ohms, are connected in series. What is their total resistance?

20 ohms
30 ohms
60 ohms
6,000 ohms

Question 7: A circuit has a 10 ohm resistor in series with a parallel combination of a 6 ohm and a 3 ohm resistor. What is the TOTAL circuit resistance?

2 ohms
9 ohms
12 ohms
19 ohms

Question 8: A "voltage divider" is a simple series circuit that:

Splits the total source voltage proportionally across two or more series resistors
Multiplies the source voltage by a fixed amount
Only works with parallel-connected resistors
Eliminates all voltage from the circuit

Question 9: For a simple two-resistor voltage divider, the voltage across R2 (the output) is found by:

Vout = Vin x R2 / (R1 + R2)
Vout = Vin x R1
Vout = Vin / (R1 x R2)
Vout = Vin + R2

Question 10: A voltage divider has a 12 V source across a 100 ohm resistor (R1) in series with a 200 ohm resistor (R2). What is the voltage across R2?

4 V
6 V
8 V
12 V

Question 11: A voltage divider has a 10 V source across two equal 50 ohm resistors (R1 and R2) in series. What is the voltage across R2?

2.5 V
5 V
7.5 V
10 V

Question 12: In a pure series section of a circuit, the current:

Is the same at every point along that series path
Splits evenly no matter how many components are present
Is always zero
Only flows through the first component

Question 13: In a pure parallel section of a circuit, the total current entering the section:

Splits among the parallel branches, with the sum of the branch currents equal to the total
Flows entirely through only one branch, ignoring the others
Is always zero in a parallel section
Doubles automatically with each added branch

Question 14: Kirchhoff's Voltage Law (KVL), applied to any complete loop within a combination circuit, states that:

The sum of all voltage drops around the loop equals the source voltage applied to that loop
All voltage drops around a loop are always exactly zero
Voltage only exists at the source, never at any resistor
KVL only applies to parallel circuits, never series circuits

Question 15: Kirchhoff's Current Law (KCL), applied at any junction (node) within a combination circuit, states that:

The total current flowing INTO the junction equals the total current flowing OUT of the junction
Current entering a junction simply vanishes
Only voltage matters at a junction, never current
KCL only applies to circuits with a single resistor

Question 16: A practical use of a voltage divider circuit is:

Producing a lower reference voltage from a higher source voltage for use elsewhere in a circuit
Generating unlimited electrical power from nothing
Increasing the source voltage beyond its original value
Converting AC to a completely different frequency

Question 17: A circuit has a 5 ohm resistor in series with a parallel combination of a 10 ohm and a 10 ohm resistor. What is the TOTAL circuit resistance?

5 ohms
10 ohms
15 ohms
20 ohms

Question 18: When TWO EQUAL resistors of value R are connected in parallel, their equivalent resistance is always:

R / 2 (half of the individual resistance)
R x 2 (double the individual resistance)
Exactly R, unchanged
Always zero

Question 19: If you add another resistor branch in PARALLEL to an existing parallel group, the overall equivalent resistance of that group will:

Decrease
Increase
Stay exactly the same
Become infinite

Question 20: If you add another resistor in SERIES to an existing series chain, the total resistance of that chain will:

Increase
Decrease
Stay exactly the same
Drop to zero

Question 21: In a two-resistor voltage divider, if R2 is made much LARGER than R1, the output voltage across R2 will be:

Close to the full input voltage
Close to zero volts
Exactly double the input voltage
Impossible to determine in any way

Question 22: In a pure parallel section of a circuit, the voltage across each branch is:

The same across every branch
Always zero on every branch
Divided equally regardless of branch resistance
Only present on the first branch

Question 23: A circuit has a 4 ohm resistor in series with a parallel combination of a 12 ohm and a 4 ohm resistor. What is the TOTAL circuit resistance?

3 ohms
4 ohms
7 ohms
16 ohms

Question 24: In a combination circuit, if a component in a purely SERIES section fails open (breaks), what happens to that whole series path?

All current flow through that path stops completely
Nothing changes at all
Current flow actually increases
Only the voltage source is affected, not the current

Question 25: If a load draws significant current from the OUTPUT point of a simple two-resistor voltage divider, the actual output voltage will typically:

Sag lower than the value calculated by the simple no-load voltage divider formula
Rise higher than the simple formula predicts
Stay exactly as the simple formula predicts, regardless of load
Become completely unrelated to the resistor values

EXAM CARD BASIC

Questions25

Time limit38 min

Pass score75%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

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Source: NEC 2026 (NFPA 70)