Series and Parallel Circuits Science 9 Series and Parallel Circuits

Objectives By the end of the lesson you should be able to: Distinguish between (and draw) series and parallel circuits Calculate current and voltage in all circuits

Lights can be connected together in different ways. Some decorative lights are connected in such a way that if one bulb burns out the rest of the lights won’t work. Lights in your house are connected so that if one bulb burns out the lights in the rest of the house will work.  

Types of Circuits These examples demonstrate the two types of circuits: Series: electrons can only flow along one path Parallel: electrons can flow along more than one path

Series Circuits There is only one pathway for current to flow. Can be recognized because there are no “intersections”

Series Circuits Current is equal everywhere in the circuit IT = I1 = I2 = I3 … Voltage is equal to the sum of the voltages of each dry cell VT = V1 + V2 + V3 …

Voltage is equal to the sum of the voltages of each dry cell VT = V1 + V2 + V3 …

Current is equal everywhere in the circuit IT = I1 = I2 = I3 …

Example: Find the unknown voltage that would be on the voltmeter and find the unknown current on the ammeter.

Parallel Circuits There are multiple pathways for current to flow. Can be recognized because there are “intersections” and the electrons have to make a “choice”

Parallel Circuits Current is equal to the sum of the current in each possible pathway IT = I1 + I2 + I3 … Voltage is equal everywhere VT = V1 = V2 = V3 …

Parallel Circuits Voltage is equal everywhere VT = V1 = V2 = V3 …

Parallel Circuits Current is equal to the sum of the current in each possible pathway IT = I1 + I2 + I3 …

Example: Find the unknown voltage that would be on the voltmeter and find the unknown current on the ammeter.

Ammeters and Voltmeters Ammeters are put into circuits in SERIES Voltmeters are put into circuits in PARALLEL

Summary Series: Total voltage is the sum of the voltage of each dry cell Current is the same at every point in the circuit Parallel: Voltage is the same in every path Total current is the sum of the current in each path

Series Circuits/Loads - Considerations Why is it impractical to wire a home/school/building with a circuit in which all loads are connected in series? If one load in a series circuit burns out, the circuit will be open, the charges will stop moving, and no loads in that circuit will work.

Parallel Circuit Loads - Considerations Why are devices in one room connected in parallel? Each can be controlled by its own switch without shutting off the others. Provide a room in your house that has objects connected in parallel.

All switches are on; therefore all appliances working Some switches off; therefore, some appliances working and some off.

Parallel Circuit Loads - Considerations Should all electrical devices in an entire home be connected to the same parallel circuit? Safety considerations? The current flowing to each device also would be flowing through the wire conductors connected to the source. This large amount of current would make wires extremely hot, possibly causing a fire.

Parallel Circuit Loads - Considerations Many separate parallel circuits are installed in buildings.

Practice Circuits 2 dry cells and one bulb all in series. 2 dry cells in parallel with one bulb. 3 dry cells in parallel with 2 bulbs. lights: 2 in parallel and 1 in series and a switch that turns all the lights off 4 dry cells: 3 in parallel and 1 in series, 6 lamps: 4 in parallel and 2 in series and 2 switches: 1 that turns off all the lights and 1 that turns off only 1 light

Practice: Do the practice circuits worksheet