Circuits

What are different types of circuits that can light up a bulb? What happens when you break each type?

The science behind current circuits is moving electric charge. Current in a river is moving water; current in a wire is moving charge. In some materials, such as metal or Fun Dough, it is very easy for current to flow. These materials are called conductors. When all charges are moving in the same direction in the conductor, there is a current. To make things super complicated, it is really the electrons moving. However, the direction of electrical current is the opposite direction of the moving electrons. If you need to draw an arrow in the direction of the current, you draw the arrow pointing “upstream” of the electron movement. It’s kind of confusing, but you can thank Ben Franklin for that. He chose to label the direction of current in this way and we’ve had to deal with his choices ever since. When you’ve made a complete circuit, current will be flowing through all the circuit elements (LEDs and “wires” made of Fun Dough). If you want to get charges moving, you need to have something to push them. That something is called the power source. In the circuits your students will be building, the power source is the two 3v coin batteries. Inside each battery, a chemical reaction creates a build-up of positive charges on the (+) end of the battery and negative charges on the (–) end of the battery. Because negative charges want to be near positive charges and away from other negative charges, as soon as there is a path for electrons from the (+) end of the battery to travel to the (–) end of the battery, the electrons will feel a push to move and—as a result— current will flow. Creating a circuit is just creating a path for those positive charges to get to the negative charges. It’s possible for a circuit to have more than one path, but there has to be at least one. If there is more than one possible path to get from one end of the power source to the other, the current can choose which path to take. When trying to figure out a path in the circuit, look at the connections and ask yourself, “What would an electron do?” Conductors such as wires allow current to flow easily. Insulators such as rubber stop current from flowing. Halfway between conductors and insulators are resistors. Resistors allow current to flow but slow it down, kind of like rocks in a river. In these circuits, the LEDs have small resistors inside them. The higher the resistance of something, the more it slows down the current. It’s always important to have at least a bit of resistance in a circuit. If there isn’t anything to slow down the current, it can go too fast and will burn out the battery and cause overheating. This is called a short circuit. When your students touch the two ends of the Fun Dough “wires'' together, they are creating a short circuit. The current doesn’t want to flow through the LED anymore because it has more resistance than the Fun Dough. Because there’s no current, the LED turns off. This activity has two types of circuits: series and parallel. Series circuits are made with all the LEDs arranged on the same path. Parallel circuits have LEDs on multiple paths, making it possible for the current to flow through one of several possible loops. When a resistor is added to a series circuit, it slows down the current. When more resistors are added, the current is slowed down even more. That’s why the LEDs in a series circuit become dimmer if more are added. If one of those LEDs were to burn out, the loop of the circuit would be broken and all of the other LEDs would go out, too. Instead, in a parallel circuit, if one LED goes out, it’s no big deal—the current can just take a different path. The final circuit your students will create is a combination of a series and parallel circuit. Pay attention to polarity. You will see a (+) symbol on the one side of your coin battery. The unmarked side is the negative (-). LEDs only allow current to flow in one direction. The current (flowing positive charges) must go in through the long leg and out through the short leg. Make sure the long leg is always closest to the (+) of the battery. Your students will be tracing out circuit diagrams with Fun Dough. Circuit diagrams are used in all electronics to identify what’s connected to what and how current will flow. It can be extremely difficult, even for the pros, to look at a circuit diagram and recreate it with wires. Wires are hard to manipulate sometimes and it can be really hard to look at a bird’s nest of wires and understand that it looks like the diagram. Hopefully by tracing it directly with Fun Dough, your students will have a better understanding of how to translate a circuit diagram into an actual circuit.

• Real world connections -
  • What kind of circuit is used to run electricity through where you live - series or parallel? (Think about whether or not turning off one light turns off the rest, or if you can have some lights on while others are off)
• Suggestions for drawing, illustrating, presenting content in creative ways
  • Use copper tape and other art supplies to make paper circuits
• Engineering and design challenges connected to the content

There are other items that can be used to make a battery for a circuit – have students explore what other items might be able to power a circuit (ex: potato, lemon etc.)