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CHAPTER 8: Ohm’s law describes the Relationship of current, voltage, and resistance. UNIT 3: Electricity

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ENERGY (E) – the ability to do work There are many forms of Energy kinetic, mechanical, chemical, solar... RECALL:

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KINETIC ENERGY POTENTIAL ENERGY Energy of motion stored Energy ex: spring, elastic band Types of Energy

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When + and – charges are pulled apart there are attractive forces wanting to put them back together, this is a form of potential energy as it has the ability to do work! Electric Potential Energy and Voltage Section 8.1 page 250

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Stored electrical energy such as that stored in a battery Electric Potential Energy

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Electrochemical Cell (Battery) Converts: Chemical Energy Electrical Energy + and – charges are separated into terminals located at either end of the cell, when connected – charges (electrons) travel towards the + (positive) terminal as the – charges repel one another

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Batteries have electric potential Energy because the stored e-’s have the ability to do work, i.e. run your CD player!

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An Electrochemical Cell Requires: different electrodes (usually metals also Carbon) And an electrolyte (electrolytic solution)

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Change in potential energy per coulomb of charge Measured in volts (V) by a voltmeter Electric Potential Difference (Voltage)

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Analogy! Stairs = the voltage Backpack = amount of charge separated More work has been done in B, therefore it has a greater Potential Energy!

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Electric Circuit A complete pathway that allows electrons to flow Transforms electrical energy into other forms of Energy Interactive website Section 8.2 Electric Current page 260

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Electric Circuit Analogy

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Parts of an Electric Circuit Conductor – wire through which current flows Load – converts electrical E into other forms of E Switch – turn circuit on or off Source – source of electrical E Interactive Website on Switches

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Circuit Diagram Symbols Interactive Website on Circuit Diagrams

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Sample Circuit Diagram

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THE CONTINUOUS FLOW OF CHARGE (ELECTRONS) IN A COMPLETE CIRCUIT Current Electricity

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the amount of charge passing a given point in a conductor per second measured in amperes (A) by an ammeter or (mA) by a galvanometer Electric Current

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Electrical Resistance: Slows down the flow of electrons and transforms electrical E into other forms of E Electrical E Light Heat Sound Motion etc Resistance & Ohm’s Law Section 8.3 page 270

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Measured in ohms (Ω) Equal to the ratio of the voltage to the current R = V/I RESISTANCE

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Current Dependent on Potential (voltage) Current Dependent on Resistance Resistance and Current Analogy:

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Factors Affecting the Amount of Resistance in a wire include : 1. Length 2. Diameter (thickness) 3. Type of wire 4. Temperature

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Resistance in a Light Bulb Long, Thin Tungsten wire Short, Thick copper wire

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The Mathematical Relationship comparing voltage (V), current (I) and resistance (R) V = I ● R Interactive websiteInteractive website SimulationSimulation Ohm’s Law

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Ohm’s Law – The VIR Tree V I R

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Various Forms of Ohm’s Law V=I●R I = V R R = V I Where: V = voltage measured in volts (V) I = current measured in amperes (A) R = resistance measured in ohms (Ω)

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STEP 1: Read and reread the question. Step up variables with known information. V = ? I= 0.5A R= 2Ω Use a question mark for the unknown value you are trying to find. Be sure to include units (V,A,Ω) Sample Problem: What voltage is used to run a flashlight with a 2 Ω resistor at a current of 0.5 A?

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STEP 3: Convert units if necessary, measurements must be in V for voltage, A for current and Ω for resistance. Fill in the information given in the question (including units). STEP 2: Determine the form of ohm’s law needed to solve for the unknown in the question. V = I●R

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V =I●R V = (0.5A)(2.0Ω) V= 1.0 V The flashlight would require a voltage of 1.0 V. STEP 4: Multiple or divide to calculate the unknown as per the formula chosen in step 3. Be sure to include units in your answer, round digits if necessary.

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Used to control CURRENT or potential difference ( VOLTAGE ) in a circuit Resistor

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RESISTANCE AND OHM’S LAW PAGE 278-9 Core lab Activity:

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