Two ways to wire a lamp
Two resistors are parts that hold current back. Joined two ways, they give different totals.
- Two resistors: 2 Ω and 3 Ω, apart.
- In series: total resistance is 2 + 3 = 5 Ω.
- In parallel: total resistance is 1.2 Ω.
Flip the wiring. Then break lamp 2.
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New words
Series — one path, part after part. Parallel — a separate path for each part.
The rule
Series has one path, so resistances add. The current is the same at every point. Parallel gives each resistor its own path, so the total resistance falls. A break in series stops everything. In parallel, only that branch goes dark.
R is the total resistance. R₁, R₂ and R₃ are the separate resistances.
Series: R = R₁ + R₂ + R₃
2 Ω and 3 Ω in series: R = 2 + 3 = 5 Ω. On a 6 V cell, I = 6 ÷ 5 = 1.2 A everywhere.
Parallel: 1 ÷ R = 1 ÷ R₁ + 1 ÷ R₂ + 1 ÷ R₃
2 Ω and 3 Ω in parallel give 1.2 Ω.
1 ÷ R = 1 ÷ 2 + 1 ÷ 3 = 5 ÷ 6
So R = 6 ÷ 5 = 1.2 Ω.
In parallel, each branch gets the same push. On a 6 V cell, the 2 Ω branch draws 3 A. The 3 Ω branch draws 2 A.
Homes use parallel wiring. Each appliance gets the full push, and it works on its own.