1. Series and Parallel Circuits
Science 9
Series and Parallel Circuits

2. 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

3. 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.

4. 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

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

6. 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 …

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

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

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

10. 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”

11. 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 …

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

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

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

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

16. 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

18. 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.

19. 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.

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

21. 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.

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

23. 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

24. Practice:
Do the practice circuits worksheet