TwiddleLab / Physics / Circuits You Can Build

Parallel: Many Paths

Lesson 6 of 10 · 7 min · Free, no account needed

What you will learn

• In parallel each branch is its own path to the battery: every branch gets the full battery voltage.
• The current splits at a junction and adds up again: battery current = sum of the branch currents.
• Switch one branch off and the others keep going. That is how homes are wired.

Start the lesson

How the lesson goes

1. At home, switching off the TV doesn't switch off the fridge. First: add a second bulb side by side. How bright is each?

   Drag the marker: 1 means as bright as one bulb alone.

2. Add bulbs side by side, each on its own branch.

   Watch the bulbs and the battery current.

3. Switch off the TV only. Keep the kitchen and the fridge on.

   In parallel every branch is a separate loop through the battery. Opening one branch leaves the other loops closed.

4. Side by side is called parallel.

   In a parallel circuit each part has its own branch, and every branch gets the full battery voltage.

   At a junction the current splits; where branches meet it adds up again: I_battery = I1 + I2 + ...

   Switch one branch off and the rest keep working.

5. Each bulb takes 0.5 A. Clip the ammeter where it reads 1 A.

   Charge is not created or lost at a junction: what flows in flows out. I_battery = I1 + I2 = 0.5 + 0.5 = 1 A.

6. Game: Wire the house. Every room's switch must work its own lamp only.

   Draw the wires. Fewest strokes wins.

7. Code: two switches can make logic. Sort each circuit: does the bulb need BOTH switches, or EITHER one?

   Series switches give one path: current flows only if switch A and switch B are closed. Parallel switches give two paths: A or B is enough.

8. A third bulb is added on its own branch. What happens to the battery current?

   Battery current = sum of branch currents. Each 3 Ω bulb on 3 V takes 1 A, so 2 bulbs need 2 A and 3 bulbs need 3 A.

9. Your house from the game. Switch on the power.

Previous lesson: Series: One Path · Next lesson: Power and Your Bill · Part of the course: Circuits You Can Build

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