Grade 9 Science: Series and Parallel Circuits PDF

Grade 9 Science, Academic Lesson #04: 11.2 Voltage and Current in Series and Parallel Circuits Learning Goals: To understand the different ways electrical circuits are designed Success Criteria: I CAN explain the difference between series and parallel circuits I CAN use circuit symbols to draw c...

Grade 9 Science, Academic Lesson #04: 11.2 Voltage and Current in Series and Parallel Circuits Learning Goals: To understand the different ways electrical circuits are designed Success Criteria: I CAN explain the difference between series and parallel circuits I CAN use circuit symbols to draw circuit diagrams I CAN explain how V, I, and R are affected by the number of loads in a circuit. Recap: ◼ Potential Difference? ◼ Current? ◼ Resistance? A Note About This Note… ◼ How is this note arranged? What do you notice about its format? ▪ Series is addressed first, then parallel ◼ Why did I do this? ▪ Easier to compare/contrast for study notes ◼ This lesson will not follow the note exactly, because it is hard to explain the concepts clearly in this order… it is however, easier to STUDY them in this order I. Series Circuits ◼ One path for electron flow ◼ Any open part stops it from flowing ◼ Total Resistance: ▪ Increases as loads are added ▪ Think of adding more hurdles on a track! II. Parallel Circuits ◼ Electrons can flow in two or more paths ◼ A break in one pathway does not affect the other pathways in the circuit. ◼ Total Resistance: ▪ decreases as loads are added ▪ **Think about adding an extra lane for traffic during rush hour! ◼ Some circuits are designed with both series and parallel components. ◼ Often switches and fuses are wired in series to control or protect the ENTIRE circuit accordingly. ◼ Symbol for fuse: Try These… 1.) Draw a circuit consisting of a 2-celled battery, a resistor, and a light bulb connected in series. Show the polarity (+ and -) of the cell and the direction of electron flow. Have a voltmeter read the resistor. (6 ) 2.) A single cell has a voltage of 1.5 V. Draw a circuit consisting of a 4.5 volt battery connected to a two light bulbs, and a resistor all connected in parallel. A voltmeter measures the potential difference across the battery. A fuse protects the entire circuit. A switch is open and controls only the resistor. The resistor is read by an ammeter. Study Tip: Can you create circuit questions for each other and compare answers??? Series Circuits: Current ◼ The current is the same throughout the series ◼ Itotal = I1 = I2 =... In ◼S I= V+ P I+ V= Series Circuits: Voltage ◼ The source of electric potential must provide enough energy/force to supply all of the loads. ◼ Loads must share the energy. ◼ Total voltage in a series circuit is the sum of the voltages across each load ◼ Vtotal = V1 + V2 +... Vn ◼ S I= V+ P I+ V= Parallel Circuits: Current ◼ Total current (“water”)in a parallel circuit is equal to the sum of the individual branch currents. ◼ Current is shared ◼ Itotal = I1 + I2 +... In ◼S I= V+ P I+ V= Parallel Circuits: Voltage ◼ The voltage or force in a parallel circuit is the same throughout. ◼ Each load uses all the potential difference supplied by the battery. ◼ Vtotal = V1 = V2 =... Vn ◼ S I= V+ P I+ V= ◼S I= V+ P I+ V= ◼ Voltage adds up in series (bulbs burn brighter) but will cells run out ◼ S I= V+ P I+ V= Series Circuits: Disadvantages ◼ The electric potential across all the components decreases when one of the components is running ◼ This affects all the other components. ◼ Example: Lights would dim when you turn on the toaster. ◼S I= V+ P I+ V= Disadvantages of Parallel Circuits ◼ increasing the number of loads increases the current ◼ the load closest to the source heats up as more appliances are turned on ◼ can cause the wires to become hot enough to start a fire. ◼S I= V+ P I+ V= ◼ Devices such as switches, fuses and resistors can be used to help prevent electrical fires. ◼ left= fuse box in an older home ◼ Right = circuit breaker box in a more modern home ◼ Fuses and circuit breakers are designed to ‘break’ on purpose when the current is too high ◼ Below is what you’d find in your house (circuit breakers are more modern, and are reusable than fuses) ◼ A blown fuse (found in a car, vs. the other type in the last slide, which is found in houses) Practice: Circuit Analysis ◼S I= V+ P I+ V= ◼ Find the missing values: Circuit Analysis ◼S I= V+ P I+ V= ◼ Find the missing values: 3 Min Review… ◼S I= V+ P I+ V= ◼ Learning Checkpoint: (Pg. 453 ) ▪ 3. What happens to the voltage in a series circuit when more loads are added? ▪ 4. What happens to the current in a parallel circuit when more loads are added? ▪ 5. How do combination circuits help prevent problems in circuits in a home? (read the text book!) ◼ **Need Help?** https://www.youtube.com/watch?v=x2EuYqj_0U k