1. Chapter 35: Electric Circuits
Conceptual Physics
Bloom High School

2. 35.1 A Battery & a Bulb
Circuit- a complete path that the electrons take
Electrons flow from the battery (dry cell) from the negative end and travel to the positive end
Electrons are provided by the battery, wires, components
Water as analogy
Battery=pump
Wires=pipe or hose
Bulb=device that operates

3. 35.2 Electric Circuits Switch- allows for a gap in a circuit
Gaps cause the electrons to stop flowing
Turns the flow on and off
Water analogy differences
Closing a circuit = turn the flow on
Opening a faucet = turning the flow on
Wires can’t “leak” like a pipe or hose
Series- devices that are connected in a row
Allows for a single path for the electrons
Parallel- devices are connected by their own ‘branch’
Allows for several paths an electron can take

4. 35.3 Series Circuits Rules of Series Circuits
1. Current flows equally through each device.
2. The total resistance of the circuit is equal to the sum of the individual resistances.
3. The current is equal to the voltage of the source divided by the total resistance. (Ohm’s Law)
4. Ohm’s Law also applies to each individual device based on its resistance.
5. The total voltage of the circuit is equal to the sum of the individual voltage drops across each device.

5. Current flows equally through each device.

6. The total resistance of the circuit is equal to the sum of the individual resistances.
The total resistance of this circuit is 18kW.

7. The current is equal to the voltage of the source divided by the total resistance. (Ohm’s Law)

8. Ohm’s Law also applies to each individual device based on its resistance.

9. The total voltage of the circuit is equal to the sum of the individual voltage drops across each device.

10. Series Circuits Disadvantages
If one device fails, the whole circuit fails
Old Christmas lights
You don’t need to use everything to use one thing
Microwave + Toaster + TV

11. Parallel Circuits Rules of Parallel Circuits
1. Each device connects the same two points of a circuit. The voltage is equal in each ‘branch.’
2. The total current is divided among the branches.
a. Path of least resistance is always taken.
Current inversely proportional to resistance
Ohm’s Law applies separately to each branch

12. Parallel Circuits Rules, part 2
3. The total current is equal to the sum of the currents.
4. As the number of branches increases, the overall resistance decreases.
Overall resistance is less than the resistance of any one branch.

13. Each device connects the same two points of a circuit.

14. The total current is divided among the branches.

15. The total current is equal to the sum of the currents.
Physics Physlet P.30.2

16. As the number of branches increases, the overall resistance decreases.

17. 35.5 Schematic Diagrams
Schematic diagrams- uses symbols to represent parts of a circuit

18. 35.6 Combining Resistors in a Compound Circuit
Is series, the resistances are added up
In parallel, the addition is more complicated
1/R=1/R1+1/R2+1/R3…
Add parallel resistances first
Make the circuit appear to be series
Add series resistances

19. 35.7 Parallel Circuits & Overloading
Homes are fed with parallel circuits from utility companies
More appliances added allows for lower resistance for the current
Greater current can occur in the wires
Overloaded- higher amount of current in wires than is safe
Fire may result
Short Circuit- a new, shorter path is offered and often bypasses regular resistance
Fuses- rated to self-destruct (melt) at a certain current level (amperage)
Circuit breakers- designed to turn off at a certain amperage

20. Circuit Breakers Increasing current boosts an electromagnets force.
When the current jumps to unsafe levels, the electromagnet pulls down a metal lever.
The linkage tilts the moving contact away from the stationary contact to break the circuit.

21. Fuses Internal wire designed to melt at a prescribed amperage
In older homes, look like a light bulb base
Most car fuses look similar to this
Other types of fuses