Exam Tip: Remember that for resistors in series the total resistance is simply the sum of each resistance.
When you see a question about “combined resistance” in a series circuit, write the formula first:
\$R{\text{total}} = R1 + R2 + \dots + Rn\$
Think of a series circuit like a single water pipe that splits into several smaller pipes and then joins back together.
All the water (current) flows through each pipe (resistor) one after the other, so the total resistance is the sum of all the individual resistances.
When resistors are connected end‑to‑end, the total resistance is:
\$R{\text{total}} = R1 + R2 + \dots + Rn\$
| Resistor | Value (Ω) |
|---|---|
| \$R_1\$ | 100 |
| \$R_2\$ | 200 |
| \$R_3\$ | 300 |
| Total | 600 Ω |
🔌 Question: Three resistors of 50 Ω, 70 Ω and 120 Ω are connected in series. What is the total resistance?
??
Answer: \$R_{\text{total}} = 50 + 70 + 120 = 240\,\Omega\$.
In a series circuit, the current is the same through every resistor.
So if the battery supplies 2 A, each resistor carries 2 A.
The sum of voltage drops across all resistors equals the supply voltage.
\$V{\text{supply}} = V{R1} + V{R2} + \dots + V{R_n}\$
Exam Tip: When a problem asks for “combined resistance” in a series circuit, you can skip the voltage or current calculations and directly use the sum of resistances.
Always double‑check that the resistors are indeed in series (no branching paths).
🔋 A 9 V battery is connected to four resistors in series: 10 Ω, 15 Ω, 25 Ω and 30 Ω.
1️⃣ Calculate the total resistance.
2️⃣ Find the current flowing through the circuit.
3️⃣ Determine the voltage drop across the 25 Ω resistor.
Use the formulas above to solve each part. Good luck! 🚀