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Electricity

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Energy Is the ability to do work Comes in 2 main types (but many forms) Potential energy is stored energy like gravity, chemical, nuclear and electrical Kinetic energy is the energy of moving objects like light, sound and mechanical Energy can be converted from one form to another

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Electrical Energy A battery holds Electrical Potential Energy (Potential, because it is stored energy) Voltage is a measure of the difference in electrical energy between 2 places in a circuit A 12 volt battery has 12 volts of potential energy difference between the positive terminal and the negative terminal

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A voltmeter measure the “potential difference” between 2 points in a circuit each volt equals 1 joule of energy per charge Voltage (symbol V) units are the volt (V)

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Electric Current is the measure of how many charges are passing a point in a circuit every second Symbol is I Unit is the Amp (A) Is measured using an ammeter

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Resistance Is a measure of how hard it is for charges to pass through an object Higher resistance means more energy is needed to pass through Resistance, voltage and current are all related If the voltage is kept the same, but the resistance is increased, the current decreases Resistance (R) is measured in ohms (symbol Ω)

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NameVoltageCurrentResistance SymbolVIR Unit (Symbol) Volts (V)Amps (A)Ohms (Ω)

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Assignment Pg 275 reading check 1,2,3,4,5,6,9 Pg 279 Checking Concepts 1,2,3,5,6 Pg 279 Understanding Key Ideas 1,2

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Ohm’s Law “the current through an object is equal to the voltage across the object divided by the resistance” I = V/R If V =6 V and R = 2 Ω then The current (I) = 6/2 = 3 Amps

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Ohms Law Use the triangle to help solve ohms law problems V= I x R I = V /R R = V/I V IR

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Ohms Law Problems 1. A 1.5 volt battery is connected to a light bulb and produces 0.5 amps of current. What is the RESISTANCE of the bulb V = 1.5 V, I = 0.5 A R = V/I = 1.5/0.5 = 3.0 ohms (Ω) 2. A different battery is put in the circuit above and the current changes to 1.5A. What is the voltage of the new battery? I=1.5 A, R = 3.0 Ω V = I x R = 1.5 x 3.0 = 4.5 V

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Now you try a couple: 1. A 6 Volt battery creates a current of 0.6 amps when connected to a motor. What is the resistance of the motor? 2. A 4.5 Volt IPod has a resistance of 900 ohms. What is the current when the ipod is turned on? V = 6.0 V, I = 0.6 A R = V/I, R = 6.0/0.6 = 10 Ω V = 4.5 V, R = 900 Ω I = V/R = 4.5/900 = 0.005 A (5 mA)

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Ohms Law Problems Handout Text book “Practice Problems” page 293 and page 294 Pg 301 #1-5, 8-10,12,13

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Circuit types Series circuits Have one pathway for electricity to flow Current decreases as more loads (resistors) are added (if voltage is kept the same) Parallel circuits Have more than one path for electricity to flow Current increases as more loads are added

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Series Circuit

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Parallel Circuit

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Circuit Analysis The voltage drop over each load sums to the voltage across the battery The current through each path sums to the current supplied by the battery In a series circuit, the voltage drop across each device can differ, but the current through each device is the same In a parallel circuit, the voltage drop across each device is the same, but the current through each device can differ.

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A Parallel Circuit

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Still needed: Static Electricity Insulators and conductors Total resistance in a series circuit How the current and voltage change as more loads are added to A series circuit A parallel circuit

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