In parallel or Series? Which way to go?

Electrical circuits can be set up in two distinctive ways – in parallel or in series. Lets see the difference between them


You’ll need:

  • The same ingredients for conductive playdough as in Light the Holidays Lights with Playdough experiment
  • LED lights, at least 3 (can be found in hardware stores)
  • 4 AA batteries (1.5V each)
  • Battery holder for 4 batteries with wires connection (can be found in hardware stores)


Make the playdoughs:

  • Mix all the ingredients in a large bowl.
  • Knead and add flour or water if needed.


Set a parallel circuit:

  • Insert the batteries into the battery holder.
  • Make 2 playdough balls.
  • Connect each ball to one of the wires, keeping them spaced out. Read the explanation in Light the Holidays Lights with Playdough to understand why the playdough balls shouldn’t touch each other.
  • Stick 2 LEDs into the balls, one leg in each ball.
  • If the LEDs don’t light, reverse their direction, and read the explanation in Light the Holidays Lights with Playdough to understand why the direction of the LED matters.
  • Now pull out one of the LEDs. What happened to the other LED?

Set a series circuit:IMG_1359a-150x150

  • Insert the batteries into the battery holder.
  • Make 3 playdough balls.
  • Set the 3 balls in a row, making sure they don’t touch each other.
  • Connect one wire to the first ball and the other to the last ball in the row.
  • Stick an LED in the first and middle balls, bridging them. Stick a second LED in the middle and last balls, bridging them. Reverse their directions, if needed.
  • Now pull out one of the LEDs. What happened to the other LED?

Mix them together: Set a circuit that contains both in parallel and series components

  • Using the series circuit set before, add another LED, bridging 2 balls.
  • if needed, reverse the directions of the LED.

What’s going on here?

Electrical circuits can be assembled in 2 basic configurations: in parallel and in series.

As you’ve seen, in a parallel circuit the components (LEDs in our case) share a common junction point. They all see the same voltage (which is a measure for energy) form the power source (the batteries in our case), no matter if we use the same component or not. However, the current (number of electrons flowing through them) depends on the components’ resistance, on how much the components oppose the flow of electron. The resistance depends on the nature on the component.

You can think of it as a multi-lane road. If one lane has pot holes, cars will drive slower in this lane, but that will not affect the speed of traffic in other lanes.

A series circuit works exactly the opposite way. The component are connected one after another in a row like train cars. The current is the same through all the components, but the voltage depends on their resistance.

In the road analogy it would look like a single lane road. When traffic moves from a well maintained section to a bumpy section, it will slow down everyone.

So the circuit looks different, but what’s all the fuss about? Remember when you pulled out one of the LEDs in the series circuit and all the lights went off? That’s because it’s a series circuit! As simple as that. When one component pulled out, the circuit is open and the electrons cannot flow.

But when you pulled out one LED from the parallel circuit it looks like it doesn’t matter, all the other components were still on. It’s true, opening the circuit in that one point doesn’t open the whole circuit and the other LEDs stay on. However, it does matter, the load on the circuit is lower now and the components left in the circuit can work with higher power.

Where do we find these circuits in our daily life?

Practically everywhere!

Some Christmas lights lines are set in series configuration. In this case, just one broken light in the line will turn off the whole line.

As an example of parallel circuit, you can think about your home. The rooms are connected in parallel to each other. Thus, turning on or off the light in one room doesn’t affect the lights in other rooms.

Did you know? Parallel and series configurations are not limited to electricity.

Our body works in parallel and series in many ways. For example, the hair connected to the head in parallel. The fall of one hair strand doesn’t affect the rest of the hair.

Parts of the blood system work in series. The same blood that goes to your toes tips travel through the torso, a leg and a foot before reaching a toe.

Now tell us:

What other applications of parallel and series configuration can you think of?