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Close the switch. What makes the bulbs brighter: more volts, fewer bulbs, or a different wiring?
Simple Circuits lab · Last updated: 16 October 2026
You close a switch and watch bulbs light up, then test what makes them brighter: more volts, fewer bulbs or a different way of wiring them. It is the same thinking electricians use when they wire a house, and it builds a feel for current, voltage and resistance.
What you'll discover
- A bulb only lights when there is a complete loop for the current to flow round.
- A higher voltage pushes more current through a bulb, so it glows brighter.
- Bulbs wired in series share the voltage and glow dimmer, while bulbs in parallel each get the full voltage.
The science in plain words
An electric circuit is a complete path that lets charge flow from one end of a battery, through the components and back to the other end. Close the switch and the loop is complete, so current flows and the bulb lights. Open it and the current stops everywhere in that loop at once.
Voltage is the push that drives the current, measured in volts. Each bulb has resistance, which opposes the current. The relationship between them is Ohm's law: current equals voltage divided by resistance. More volts across the same bulb means more current, and a bulb's brightness depends on the power it receives, so it glows brighter.
How the bulbs are wired matters. In a series circuit the bulbs sit one after another in a single loop. The total resistance goes up and the battery's voltage is shared between them, so each bulb is dimmer, and if one breaks they all go out. In a parallel circuit each bulb has its own branch connected straight across the battery. Each bulb gets the full voltage and glows as brightly as a single bulb would, and one failing does not switch off the others. That is why homes are wired in parallel, although more branches draw more current from the battery, so it runs down faster.
Where it fits
Common questions
What is the difference between series and parallel circuits?
In a series circuit components are connected one after another in a single loop, so the same current flows through all of them. In a parallel circuit each component has its own branch across the battery, so each gets the full voltage and can work independently.
Why are bulbs dimmer when you add more in series?
Each extra bulb adds resistance to the single loop, so less current flows, and the battery's voltage is shared between all the bulbs. Each one receives less power, so every bulb in the chain glows more dimly than one bulb on its own.
Why are houses wired in parallel?
Parallel wiring gives every appliance the full mains voltage and lets each one be switched on or off without affecting the others. If one bulb fails, the rest keep working. In a series circuit a single broken bulb would switch off everything in the loop.
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Try it yourself
The Simple Circuits lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.