Series and Parallel Circuits

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Updated on Jan 10, 2014

It used to be that if you had a string of holiday lights and one bulb went out, the whole string no longer worked. This was because the lights were set up in a series circuit. Recently, companies have started producinglights and other electronics thatare set up in parallel circuits. Circuits carry electric current when they are in a closed loop, and can act differently depending on the physical set up of the circuit. Current, which is the flow of electrons in a circuit, can be carried through wires, barriers, and any functional pieces of circuits, like lights.

Ohm’s law is an equation that describes the relationship between voltage (electric force), current (electron flow) and resistance (the resistance of an object to passing electric current).

I = V / R

Where V is voltage, measured in volts (V), I is current, measured in amperes (A), and R is electrical resistance, measured in ohms (Ω)

In a series circuit, the parts of the circuit are in a row, one after the other so current flows through them. Parallel circuits are set up so that the current has an independent path to take through each piece. For holiday lights, this means one bulb can burn out and not affect the rest of the circuit.


Are bulbs in a parallel or series circuit brighter?


  • 9V battery
  • Tape
  • Aluminum foil
  • 2 identical flashlight bulbs


  1. Tape an 8-inch strip of aluminum foil to the positive terminal of the 9V battery. Make sure the aluminum foil is touching the metal.
  2. Tape another 8-inch strip of aluminum foil to the negative terminal of the 9V battery.
  3. Wrap the end of the aluminum strip attached to the positive terminal around the light bulb’s metal screw cap.
  4. Take a 4-inch strip of aluminum foil and wrap one end around the second light bulb.
  5. Place the bottom of the light bulb attached to the positive terminal on the loose end of the other battery’s foil strip.
  6. Place the bottom of the second light bulb on the foil strip attached to the negative terminal.
  7. You have created a series circuit. Take note of how brightly the bulbs shine.

Series Circuit

  1. Now, let’s create a parallel circuit. First, remove the light bulbs from the system.
  2. Take two 4-inch strips of aluminum foil and fold one of each of the ends around the strip coming off the positive terminal of the battery. It should look like the rungs of a ladder, but only connected on one side.
  3. Wrap the loose ends of the 4-inch strips around the metal screw cap of each light bulb.
  4. Place the bottom of each of the light bulbs against the foil strip attached to the negative terminal.

Parallel Circuit

  1. Record your observations, comparing the brightness of the two circuits you created.


The bulbs in parallel circuit will be brighter than the bulbs in series circuit.


In parallel circuits, each independent path experiences the same voltage drop. For series circuits, the voltage drop is split between the components (lights, for example) depending on their resistances. Bigger voltage drops draw a larger current, which means more electrons flow through the bulb, making it brighter.

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