Lesson page
Lesson 3: Series and Parallel Circuits
Read the lesson, then answer the multiple-choice practice set below. You get instant right or wrong feedback with explanation.
Electrical Calculations Electrical Theory
Lesson Content
This lesson helps you translate circuit behavior into quick exam answers. Series and parallel are basic ideas that appear in many different forms.
Japanese Key Term
複線図（ふくせんず / multi-line wiring diagram）
Hiragana
ふくせんず
English Meaning
Multi-line wiring diagram
Simple Explanation
In series circuits, values add in a straight path. In parallel circuits, the current divides and the total resistance behaves differently.
Detailed Explanation
Many written exam questions hide circuit behavior inside a short sentence. If the circuit is series, current stays the same and resistance adds. If it is parallel, voltage stays the same across branches and current divides. Memorize these patterns before trying harder calculation questions.
Key Vocabulary
- 単線図（たんせんず / single-line diagram）
- 複線図（ふくせんず / multi-line wiring diagram）
- 直列（ちょくれつ / series）
- 並列（へいれつ / parallel）
Formula
Series: Rtotal = R1 + R2 + R3nParallel: 1 / Rtotal = 1 / R1 + 1 / R2 + 1 / R3
Worked Example
Two resistors, 4 Ω and 6 Ω, in series make 10 Ω total. In parallel, the total resistance is lower than either single resistor.
Exam Tips
If the question says the current has several paths, think parallel. If the current has one path, think series.
Common Exam Trap
A parallel circuit does not add resistances the same way as a series circuit.
Site Reality in Japan
On site, wiring diagrams and actual branch connections must match. The written exam checks whether you can read both.
Practice Question
What is total resistance for two series resistors of 3 Ω and 7 Ω?
Answer
10 Ω
Explanation
In series, resistance adds directly: 3 + 7 = 10 Ω.
1. This style of drawing usually tests your ability to:
L1 ---[Load A]--- N L2 ---[Load B]--- N
Separate branch paths with labeled loads are used to test circuit tracing and assignment accuracy.
2. Why do both L and N pass through the RCD/ELCB block?
L ---[MCB]---[RCD/ELCB]--- Branches N --------------[RCD/ELCB]--- Branches
Leakage devices compare line and neutral current balance; imbalance indicates leakage path.
3. What exam skill does this pair of notations test?
[Single-line] DB -> SW -> Lamp [Multi-line] L -> SW -> Lamp -> N
The candidate must translate between simplified and detailed conductor representations correctly.
4. If Outlet 1 fails open at its load, Outlet 2 is usually:
L ---+---(Outlet 1)
+---(Outlet 2)
N ---+---(Outlet 1/2)
In a parallel branch arrangement, one load open-circuit does not necessarily interrupt other branches.
5. Primary purpose of the PE line here is:
PE ------------------------(Metal case) L,N -----------------------(Appliance)
PE is for protective earthing and fault-current safety, not normal operating current.
6. With SW1 open, the expected state is:
L --[SW1]--+--(Lamp A)--N
+--(Lamp B)--N
SW1 is upstream of both branch lamps, so opening it removes supply to both.