1. Series & Parallel Circuits
Chapter 23
Physics
Series & Parallel Circuits

2. Series Circuits - 1 ONE path for electrons to flow
If one component goes out, they ALL go out
The current is the same everywhere in the circuit
The voltage & resistance change at each component
The arrow symbols in the diagram are ammeters. They should ALL READ THE SAME. There is no where else for the flow of electrons to go and no reason for it to be different.

3. Series Circuits - 2
The voltage provided by the source (battery) is equal to the sum of the voltage drops across the resistors/lamps
Vsource = VA + VB + …
Add this equation to their card under a label that says SERIES CIRCUITS. This means that the first light bulbs in a circuit might get more voltage and thus be brighter than lighter light bulbs.

4. Series Circuits - 3
Equivalent Resistance – Total resistance in the whole circuit
REq = RA + RB + …
Current:
I = Vsource / Req
Voltage Dividers – drop the voltage to a desired amount by using up some of it
Add these to the same location on the card

5. Series Circuits – Problem 1
(p 619 #1) Three 20 Ω resistors are connected in series across a 120 V generator.
What is the equivalent resistance of the circuit?
What is the current in the circuit?
60 Ω, 2 A

6. Series Circuits – Problem 2
(p 619 # 2 & 5) A 10 Ω, 15 Ω, and 5 Ω resistor are connected in a series circuit with a 90 V battery.
What is the equivalent resistance of the circuit?
What is the current in the circuit?
What is the voltage drop (used up) across each of the 3 resistors?
30 Ω, 3 A, 30 V, 45 V, 15 V

7. Series Circuits – Problem 3
(p 619 # 4) A string of holiday lights has 10 bulbs with equal resistances connected in series. When the string of lights is connected to a 120 V outlet, the current through the bulbs is 0.06 A.
What is the equivalent resistance of the circuit?
What is the resistance of each bulb?
2000 Ω, 200 Ω

8. Parallel Circuits - 1 MANY paths for the electrons to flow
Each “branch” is independent, so changing or removing one light doesn’t effect the others

9. Parallel Circuits - 2 The voltage everywhere is the same.
The current through each branch is determined by its resistance.
Equivalent Resistance:
1/REq = 1/RA + 1/RB + …
Add this equation under Parallel Circuits Label on card.

10. Parallel Circuits – Problem 1
(p 625 Ex 3) Three resistors, 60.0 Ω, 30.0 Ω, and 20.0 Ω, are connected in parallel across a 90.0 V battery.
Find the current through each branch of the circuit.
Find the equivalent resistance of the circuit.
Find the current through the battery. (Total current for entire circuit.)
1.50 A, 3.00 A, 4.50 A, 10.0 Ω, 9.00 A

11. Parallel Circuits – Problem 2
(p 626 # 15) Three 15.0 Ω resistors are connected in parallel and placed across a 30.0 V battery.
What is the equivalent resistance for the circuit?
What is the current through the entire circuit?
What is the current through each branch of the circuit?
5.00 Ω, 6.00 A, 2.00 A

12. Safety Devices in Circuits - 1
Fuses
Metal strip melts when the current becomes too high for the circuit
Fuse is placed there because when it goes out, all the branches stop working. The fuse is in SERIES to the rest of the circuit.

13. Safety Devices in Circuits – 2
Circuit Breakers
Reusable fuses
When a circuit is ‘overloaded’ the breaker opens

14. Safety Devices in Circuits - 3
Ground-fault interrupter
Detects small differences in current caused by an extra path and opens the current
Extra path is usually water. These are in most kitchens and bathrooms
Short Circuit
Low resistance (too short of a path) in the circuit causes too much current
Wires get hot and could start a fire
Draw a circuit on the board. Show it shorted. Explain that this is the #1 problem with chaney kits.