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Voltage: Parallel and Series Circuits (2019)
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1. Introduction: LED Sign -
2. Failed Series Circuit
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Check Your Understanding: Failed Series Circuit -
Mini-Project: Voltage Investigation
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3. Parallel Circuits
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Upload a photo of a parallel circuit used to power multiple independent loads. -
Mini-Project - Shared Voltage Nodes
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Check Your Understanding: Shared Voltage Nodes
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Wire Coloring
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Check Your Understanding: Parallel Circuits
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4. Power Panels - Managing Parallel Circuits
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Mini-Project: Mounting to the Terminal Block
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Mini-Project - Terminal Block with Jumper
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Check Your Understanding: Power Panels
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Unit Project: LED Sign
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Upload Photo: LED Sign
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Upload Block Diagram: LED Sign
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Shared Voltage Nodes
Mini Project Shared Voltage Nodes
Build the circuit shown here. Construct the three-way connection by clipping multiple alligator clips together.
Parallel Circuit
Explanation
Even though it looks quite different, this circuit and the previous one you built are electrically very similar.
Because electricity travels very freely through wires, all points in a circuit that are directly connected by wire act like the same "piece" from a voltage perspective. This is because, when there is a good conductor between them, no voltage is used up when electricity flows from one of those points to the other.
Example: No voltage is used up getting electricity between point A and B on the diagram. That means whatever voltage level is at A is also at B, and vice versa.
The whole connected region of wire forms a single "node" with the same shared voltage level.
Thus, the 3.3V from the positive terminal on the battery is also available at the positive terminals of both LEDs.
When this circuit is powered, both LEDs light.
Think back. Notice that series circuits don't have the same shared voltage node that the parallel configuration has.
Each LED draws voltage in turn, and thus there was not enough voltage to make the circuit work in serial configuration.
Use the multimeter in voltage mode to check the voltage "across" each of the LEDs. What voltage difference do you expect to see? Is that what you actually see?
Use the multimeter in voltage mode to check the voltage at different points in the same "shared voltage node" (for example, A and B in the diagram below). What voltage difference do you expect to see? Is that what you actually see?
Try It: Remove an LED...
Try removing one of the LEDs from the circuit. Keep its portion of the circuit "open" (unconnected).
What happens when you remove one of the LEDs?
Try It: Reconnect with a wire...
Now close the connection where the LED used to be by reconnecting the wires that used to go to the LED.
What happens to the the remaining LED?
Explanation
Parallel circuits "split" the flow of electrical power between branches. Even though there is the same amount of "push" for each of them, the actual amount of electricity that flows can be different. When both LEDs were connected, both paths had the same amount of resistance, and electricity flowed evenly between them. When one was removed, the electricity had only one path to go down. When the second path was reconnected, electricity had two paths to go down, but one was much easier, and so nearly all the electricity went that way instead?
Note: Similar, but not identical!
While the circuit in this mini-project is identical to the earlier version in terms of voltage, it is not quite identical in terms of electrical flow ("current").
This is because the electrical power for both LEDs pass through a single wire before splitting in half (and again after the two paths merge).
While this does not affect the behavior of the circuit, it does mean you need to pay attention to the wires you use. There is twice as much electricity flowing through some parts of the circuit as others! It's not a big deal with small LEDs and coin cell batteries, but larger batteries and motors could be damaged.
We will discuss this more in the next chapter, which features those larger batteries and motors!