The way you connect components in a circuit changes everything — how bright your bulbs glow, how long your batteries last, and even whether one broken wire plunges your whole house into darkness. Australian homes are wired almost entirely in parallel, while old-fashioned Christmas lights were wired in series. In this lesson, you will discover why engineers made that choice.
You have two identical bulbs and a 9 V battery. In Circuit A, the bulbs are connected one after another (series). In Circuit B, they are connected side-by-side (parallel). Which circuit will make the bulbs brighter? And if one bulb burns out, which circuit keeps the other bulb lit? Draw your prediction for each, then verify with the interactive diagrams below.
In a series circuit, components are connected end-to-end in a single path. The current has only one route to take.
Key properties:
Real-world example: Old-fashioned Christmas tree lights were wired in series. When one bulb blew, the entire string went dark — and you had to test each bulb to find the culprit. Modern LED strings use parallel wiring or special shunt wires to avoid this problem.
In a parallel circuit, components are connected across the same two points, creating multiple paths for current.
Key properties:
Real-world example: Every powerpoint in your home is connected in parallel. When you turn off the kitchen light, your phone keeps charging. When you plug in another device, it gets the same 240 V as everything else — but the total current drawn increases.
| Property | Series Circuit | Parallel Circuit |
|---|---|---|
| Current | Same everywhere | Splits between branches |
| Voltage | Shared across components | Same across each branch |
| Total resistance | Rtotal = R1 + R2 + ... | 1/Rtotal = 1/R1 + 1/R2 + ... |
| Brightness (identical bulbs) | Dimmer (voltage shared) | Brighter (full voltage each) |
| If one component fails | All stop | Others keep working |
| Adding more components | Current decreases | Total current increases |
| Real-world use | Old Christmas lights, some sensors | Home wiring, car electrics, solar arrays |
Series Circuit — 2 Bulbs with 9 V Battery
Each bulb gets 4.5 V (voltage shared). Same current flows through both. If one bulb breaks, both go out.
Every powerpoint, light switch, and appliance in an Australian home is connected in parallel to the 240 V mains supply. This design is not accidental — it is essential for safety, convenience, and consistent performance.
If homes were wired in series, turning off the bedroom light would cut power to the entire house. The refrigerator would stop when the TV turned off. And every device would receive a fraction of 240 V — a toaster designed for 240 V would barely warm up if it only got 20 V because 11 other appliances were sharing the voltage.
Solar panels are also wired in parallel arrays. A typical rooftop installation has 10–20 panels, each producing ~40 V. When connected in parallel, the array maintains ~40 V but delivers more current. An inverter then converts this DC to 240 V AC for home use. If one panel is shaded and underperforming, parallel wiring ensures the others continue producing at full capacity — just like a parallel circuit should.
The National Electricity Market (NEM) itself operates on parallel principles. Multiple power stations (coal, gas, wind, solar) all feed into the same grid voltage. When one station goes offline for maintenance, the others continue supplying power — the grid does not "go out" because one generator stopped.
The total resistance of a circuit depends on how components are connected:
Example: Two 10 Ω resistors in series give R = 20 Ω. The same two in parallel give 1/R = 1/10 + 1/10 = 2/10, so R = 5 Ω. Parallel connections always reduce total resistance because they provide more paths for current.