Answer Question in your Notes DO NOW ID on Answer Question in your Notes How does the electricity work in your house?

Unit 4: Electricity Chapter 13: Electrical Systems 13.1 Series Circuits 13.2 Parallel Circuits 13.3 Electrical Power, AC and DC Electricity 20 minute notes (Print out has questions + 5 minutes)

SWBAT compare series and parallel circuits. Objective: Date SWBAT compare series and parallel circuits.

In parallel circuits the current can take more than one path.

Kirchhoff’s Current Law All of the current entering a branch point must exit again.

Voltage and parallel circuits If the voltage is the same along a wire, then the same voltage appears across each branch of a parallel circuit.

Voltage and parallel circuits Parallel circuits have two advantages over series circuits: Each device in the circuit has a voltage drop equal to the full battery voltage. Each device in the circuit may be turned off independently without stopping the current in the other devices in the circuit.

Resistance in parallel circuits Adding resistance in parallel provides another path for current, and more current flows. When more current flows at the same voltage, the total resistance of the circuit must decrease.

Store Example Problem: One lane is open and the store is busy. Rate of people leaving the store is slow with one lane. If a second register opens, half of the people can pass through each lane. The total flow of people from the store is higher.

Calculating resistance in parallel circuits A circuit contains a 2-ohm resistor and a 4-ohm resistor in parallel. Calculate the total resistance of the circuit. 1/Rtotal = ½ + ¼ = 0.5+0.25 1/Rtotal = 0.75 1 = Rtotal x 0.75 1/0.75 = Rtotal

Calculating resistance in parallel circuits A circuit contains a 2-ohm resistor and a 4-ohm resistor in parallel. Calculate the total resistance of the circuit. Looking for: …the resistance Given: …the type of circuit (parallel) and branch resistances (2  and 4 ) Relationships: Use: the rule for parallel resistances. Solution: 1/Rtotal = ½ + ¼ = 0.5+0.25 1/Rtotal = 0.75 1 = Rtotal x 0.75 1/0.75 = Rtotal

Current and parallel circuits Each branch works independently so the total current in a parallel circuit is the sum of the currents in each branch.

Parallel vs. Series – Complete the Table Use Pencil or leave space to add to your answers Remember: series/same/current; parallel/same/voltage. Use Ohm’s law for both.

Short circuits A short circuit is a parallel path in a circuit with very low resistance. A short circuit can be created accidentally by making a parallel branch with a wire. Review from 13.1 Notes for Lab

Fuses In newer homes, flip the tripped circuit breaker. In older homes you must replace the blown fuse. Fuses are also used in car electrical systems and in electrical devices such as televisions or in electrical meters used to test circuits.

13.2 Investigation: Parallel Circuits Key Question: How do parallel circuits work? Objectives: Build parallel circuits. Compare and contrast series and parallel circuits. Discuss applications of parallel circuits.

Review Questions