Series and Parallel Circuits | Physics

📖 In-Depth Theory

Series Circuits

In a SERIES circuit, all components are in a SINGLE LOOP — one path for current.

Rules:

CURRENT: same through every component — I₁ = I₂ = I₃

PD: splits between components — V_total = V₁ + V₂ + V₃

RESISTANCE: adds up — R_total = R₁ + R₂ + R₃

EXAMPLE:

R₁ = 4 Ω, R₂ = 6 Ω, battery = 10 V.

R_total = 10 Ω. I = 10 ÷ 10 = 1 A.

V₁ = 1 × 4 = 4 V; V₂ = 1 × 6 = 6 V. Check: 4 + 6 = 10 V ✓

If one component breaks — ALL components stop working.

Parallel Circuits

In a PARALLEL circuit, components are in SEPARATE BRANCHES — multiple paths for current.

Rules:

PD: same across every branch — V₁ = V₂ = V₃ = V_supply

CURRENT: splits — I_total = I₁ + I₂ + I₃

RESISTANCE: total is LESS than the smallest individual resistance.

EXAMPLE:

12 V supply. R₁ = 6 Ω, R₂ = 4 Ω.

I₁ = 12 ÷ 6 = 2 A; I₂ = 12 ÷ 4 = 3 A.

I_total = 2 + 3 = 5 A.

If one branch breaks — OTHER branches continue working.

Why Household Circuits Are Parallel

Domestic wiring is PARALLEL because:

1. Each appliance gets the FULL mains pd (230 V).

2. Appliances work INDEPENDENTLY — switching one off doesn't affect others.

3. Easy to add appliances without affecting existing ones.

4. Each appliance can have its own fuse.

SECOMPARISON:

Series: same current, pd splits, R adds, all-or-nothing.

Parallel: same pd, current splits, R decreases, independent operation.

⚠️ Common Mistake

In PARALLEL, total resistance is LESS than any individual resistance — more branches = more paths = lower resistance. Adding resistors in SERIES always increases total resistance. Students often mix these up.

📐 Variables

ICurrent (I) is measured in amperes (A)

VPotential difference (V) is measured in volts (V)

RResistance (R) is measured in ohms (Ω)

📐 Key Equations

Series: R_total = R₁ + R₂ + R₃

Series: V_total = V₁ + V₂ + V₃

Parallel: I_total = I₁ + I₂ + I₃

📌 Key Note

Series: same I, pd splits, R adds. Parallel: same pd, I splits, total R less than smallest. Household = parallel — full voltage, independent. Series break = all stop. Parallel break = others continue.

🎯 Matching Activity — Series vs Parallel

Match each property to the correct circuit type. — drag the symbols on the right to match the component names on the left.

Series

Drop here

Parallel

Drop here

Series

Drop here

Parallel

Drop here

Both

Drop here

Current is identical at every point in the loop

If one component breaks, the others continue working

Potential difference is the same across every branch

The battery provides the total pd for the whole circuit

Total resistance equals the sum of individual resistances

⚽ FIFA Worked Examples

Series Circuit

R₁ = 3 Ω and R₂ = 7 Ω in series with a 20 V battery. Find the current and pd across each resistor.

F

R_total = R₁ + R₂; I = V ÷ R_total; V₁ = I × R₁; V₂ = I × R₂

I

R_total = 3 + 7 = 10 Ω; V = 20 V

F

I = 20 ÷ 10 = 2 A; V₁ = 2 × 3 = 6 V; V₂ = 2 × 7 = 14 V

A

I = 2 A throughout; V₁ = 6 V; V₂ = 14 V (check: 6 + 14 = 20 V ✓)

🧪 Required Practical

🔬 RP15 (Physics) — Construct series and parallel circuits; measure I and V at different points to verify rules.

Know the method, variables, equipment and how to analyse results.

🎯 Test Yourself

Question 1 of 2

1. Two lamps are connected in parallel across a 6 V battery. What is the pd across each lamp?

2. Why is household wiring parallel rather than series?

⭐ How Well Do You Understand This Topic?

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⚡ Series and Parallel Circuits

Series Circuits

Parallel Circuits

Why Household Circuits Are Parallel

🔬 RP15 (Physics) — Construct series and parallel circuits; measure I and V at different points to verify rules.

Mr. Badmus AI