ELECTRIC CURRENT AND CIRCUITS TOPIC 1 – ELECTRICAL ENERGY AND VOLTAGE TOPIC 2 – CAPACITANCE TOPIC 3 – CURRENT AND RESISTANCE TOPIC 4 – ELECTRIC POWER TOPIC 5 – EQUIVALENT RESISTANCE AND CIRCUITS

Learning Goal: You will understand how to find the equivalent resistance of a circuit an how to determine the current, voltage, and power at different parts of the circuit. Success Criteria: You will know you have met the learning goal when you can truthfully say: 1.I can determine the equivalent resistance of multiple resistors. 2.I can determine the power, voltage, and current at different places in a circuit. Image(s) from Bing Images

Success Criteria 1: I can determine the equivalent resistance of multiple resistors A circuit is an electrical system where current is able to flow. A flashlight is a simple circuit consisting of a battery and a light bulb. A computer is a complex circuit with huge numbers of components. Image(s) from Bing Images

Success Criteria 1: I can determine the equivalent resistance of multiple resistors Electrical devices can be wired in series or in parallel. When wired in series, they come one after the other in the same loop. When wired in series, the equivalent resistance (R eq ) is found by adding together the resistances of everything in the series. R eq = R 1 + R 2 + R 3 + … When wired in parallel, they form multiple paths that complete the circuit. Since adding multiple pathways makes it easier for electricity to flow, placing electrical devices in parallel actually decreases the overall resistance. For parallel circuits, you can find the R eq using: 1/R eq = 1/R 1 + 1/R 2 + 1/R 3 + … which can also be written as: R eq = (R R R …) -1 Image(s) from Bing Images

Success Criteria 1: I can determine the equivalent resistance of multiple resistors For example: a 2 Ω resistor, and a 3 Ω ohm resistor wired in series would have a R eq of: R eq = R 1 + R 2 = 2 Ω + 3 Ω = 5 Ω A 2 Ω and a 3 Ω resistor wired in parallel would have a R eq of: R eq = (R R 2 -1 ) -1 = (2 Ω Ω -1 ) -1 = 1.2 Ω Task (6 points): Find each R eq. When sketching the circuits, use the symbols you just learned. Series R eq SketchParallel R eq Sketch a) A battery connected to a 10 Ω light bulb and a 6 Ω light bulb. b) A battery connected to a 5 Ω resistor, a 12 Ω resistor, and a 20 Ω light bulb. c) A battery connected to a 1.3 Ω resistor, a 24 m Ω resistor, a 782 m Ω light bulb, and a k Ω resistor. Image(s) from Bing Images

Success Criteria 1: I can determine the equivalent resistance of multiple resistors Sometimes circuits have resistors wired in both series and parallel arrangements. In these cases: 1.Find the R eq of each section that is wired in series. 2.Find the R eq of each section that is wired in parallel. 3.Find the R eq of a larger section that is wired in series. 4.Find the R eq of a larger section that is wired in parallel. Put another way, find the R eq of the smallest sections first, then larger, then larger… Image(s) from Bing Images

Success Criteria 1: I can determine the equivalent resistance of multiple resistors Task (5 points): Suppose R 1 = 3 Ω, R 2 = 5 Ω, R 3 = 2 Ω, R 4 = 8 Ω, R 5 = 3.2 Ω, and R 6 = 6.5 Ω. Find the R eq of each of the following sections of the circuit. a)R 2 and R 3. b)R 2, R 3, and R 1. c)R 4 and R 5. d)R 4, R 5, and R 6. e)R eq of the whole circuit. Image(s) from Bing Images

Success Criteria 1: I can determine the equivalent resistance of multiple resistors Task (4 points): Find the R eq for each of the following circuits. For now, skip finding the voltage, current, and power at the various labeled places around the circuits. a) b)

Success Criteria 1: I can determine the equivalent resistance of multiple resistors Task (28 points): Find the R eq for each of the following circuits. For now, skip finding the voltage, current, and power at the various labeled places around the circuits. c) d)

Success Criteria 2: I can determine the power, voltage, and current at different places in a circuit. The voltage across each resistor in a series is directly related to what fraction of the resistance in that series is supplied by that resistor. This keeps the current the same along one path in a circuit. In a parallel circuit, the voltage across each path is the same. The current is higher where the resistance is lower. Once you know the resistance and the voltage, you can use V = IR to find the current and P = IV = I 2 R = V 2 /R to find the power. Note: When batteries are added in series, their voltages are added together (Ex: 9 V + 9 V = 18 V).

Success Criteria 2: I can determine the power, voltage, and current at different places in a circuit. Task (4 points): Fill in the blanks. a)All of the points within one loop on a circuit have the same ___________. b)All of the loops in a circuit that are in parallel with each other have the same ____________. c)If a certain resistor contributes 1/5 of the total resistance in a series, the voltage across that resistor will be ____________ of the total voltage across that series. d)Whichever path through a circuit has the least resistance will have the greatest ____________. Task (28 points, continued): Consider again the circuits from Task Find the rest of the wanted information.

Task (4 points): Write at least 8 things you learned in this topic (1/2 point each). If you do this in your notebook, please do it in list form, rather than paragraph form. Image(s) from Bing Images