Series and Parallel Circuits

In this tutorial, we’ll learn about two fundamental types of circuits - series and parallel circuits - and find out how to apply them to most efficiently light up multiple LEDs (because more lights = more fun!)

Let’s say we have a circuit with a single LED (as shown in the leftmost circuit in the editor), but we now want to be able to light up more than one light. Your first thought may be to add another LED directly to the circuit, chaining it to an existing LED as shown in the middle circuit.

This configuration is known as a series circuit, where there is a single path for current to flow from the positive side of the battery to the negative side, and thus the amount of current through each component is the same. We're also using a new tool called a multimeter that lets us measure current (A), voltage (V), and resistance (R) in a circuit.

Let’s see what happens when we test out this design.

1. Start the simulator.
2. Notice how with the middle circuit, the LEDs seem to barely turn on. This is because LEDs have a forward voltage typically around 2V. If we have two LEDs requiring 2V, that's a total voltage drop of 4V, which is greater than our current 3V battery can supply! Check out the multimeter readings: The voltage from the battery is currently being split across the two LEDs, providing only 1.5V to each, when they require 2V to light up. This is why there is no current flowing through the circuit (0A).
   
3. Continue to the next step, where we’ll see how we can rearrange the LEDs in a parallel configuration to solve this problem.

In the rightmost circuit, the LEDs are arranged in parallel. Notice how each LED has one leg that has a path to the negative side of the battery, and another that has a path to the positive side of the battery. When components are arranged in this way, the current from the battery splits into each of these paths, while the voltage across each LEDs is the same.

1. Click "Start Simulation" to test the circuit. Notice how all of the LEDs can be powered in this way – and that we can power many more than just 2!
2. Let's measure the voltage across any of the LEDs using a multimeter. Add a multimeter by clicking on “+ Components,” clicking on the multimeter, and adding it to your circuit. Connect one leg of the multimeter to one side of the left leg of an LED, and the other end to the right leg of the LED. Make sure that the multimeter is set to measure voltage by clicking on the “V” button on the multimeter.
3. Start the simulation and see how much voltage is dropped across the LED. How does this voltage compare to that in the series circuit?
4. Continue to the next step

You’ve learned about some of the basic differences between series and parallel circuits, as well as how to effectively and safely power multiple LEDs!

Continue Tinkering

• Practice hooking up LEDs in parallel by adding additional LEDs to the parallel circuit.
• Can you think of another way to power the LEDs in the series circuit? You can try changing the battery type, or adding additional batteries in series (remember, voltages should add up in a series circuit). You may have to adjust the resistor value to account for different batteries. Try it out!