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It’s Electric! Chapter 17 Electricity Chapter 17 STANDARD S8P5: Students will recognize characteristics of gravity, electricity, and magnetism as major kinds of forces in nature. b.Demonstrate the advantages and disadvantages of series and parallel circuits and how they transfer energy. c. Investigate and explain that electric currents and magnets can exert a force on each other. Chapter 17 WARM-UP 2-22-12 Matter that flows to fit into a container includes: A. Solids and liquids B. Liquids only C. Gases and solids D. Liquids and gases Which phase has the least density? A. Solid B. Gas C. Liquid WARM-UP 2-22-12 Which of these factors affects the temperature at which water boils? A. The size and shape of the pot in which the water is heated. B. The atmospheric pressure at which the water is heated. C. The amount of heat added to the water D. The temperature of the water before it is heated WARM-UP 2-22-12 Which of the following occurs when a liquid becomes a gas? A. The particles give off energy B. The particles break away from one another C. The particles move closer together D. The particles slow down. Chapter 17 ESSENTIAL QUESTION What are the essential elements of a circuit? ? Path Finders Using the materials at your table, test each set-up and decide which ones work and which ones don’t. Answer the Path Finders questions in your journal. Chapter 17 CIRCUIT An uninterrupted pathway or loop through which electricity can flow (usually wire pathway) Chapter 17 ELECTRIC CIRCUIT What are the essential elements of a circuit? What are the essential elements of a circuit? 1.An uninterrupted pathway – good conductor like wires 2.Energy Source – to “push” the electrons 3.Electrical Device or Load – changes the electric energy into another form of energy Parts of a Circuit Chapter 17 Parts of an Electric Circuit • A Switch to Control a Circuit Sometimes, a circuit also contains a switch. A switch is used to open and close a circuit. Parts of a Circuit Please note – although switches are found in my circuits, they are not an essential part of a circuit! Chapter 17 Types of Circuits • Series Circuits: A series circuit is a circuit in which all parts are connected in a single loop. • Uses for Series Circuits: Series circuits are useful in wiring burglar alarms. If any part of the circuit fails, there will be no current in the system and the alarm will sound. Chapter 17 Types of Circuits • Parallel Circuits: A parallel circuit is a circuit in which loads are connected side by side. • Uses for Parallel Circuits: Almost all appliances are built with parallel circuits so that they will keep working if part of the system fails. What happens if the pathway is broken? The electricity will not flow… you will have a “break” in the pathway. What is a Short Circuit? An unintended path connecting one part of a circuit with another. CONSIDER THIS… What is the difference between static electricity and current electricity? Chapter 17 RESPONSE… Static electricity is stationary or collects on the surface of an object, whereas current electricity is flowing very rapidly through a conductor. Chapter 17 Why does Current Electricity FLOW? Chapter 17 Flow of Electricity #1 Electric charges flow from an area of high voltage (a lot of excess electrons) to an area of low voltage (lower number of electrons). What makes the water flow in figure A? Apply this answer to figure B using negative charges instead of water. Water pressure and voltage behave in similar ways. Thermal Energy and Electrical Energy Behave in Similar Ways Thermal energy flow from high concentration (warm) to low concentration (cool) until equilibrium is reached. Electricity flows from high concentration (extra negative electrons) to areas of low concentration (deficient of electrons = positive area). Both flow from “high to low”. Flow of Electricity #2 The flow of electricity in current electricity has electrical pressure or voltage. (Push or pull from electric force) Flow of Electricity #3 Electricity can only flow when there is a closed pathway for the charge to flow through How Does Electricity Flow? Current (flowing electrons) always follow the path of least resistance. How is the flow of electricity similar to the flow of water through a pipe? Both require a closed path or pipe. If the pipe is broken or the wire is broken, NO FLOW… Chapter 17 Circuit Terminology Essential Terms: 1.Circuit 2.Electrical Current 3.Voltage 4.Resistance Chapter 17 REMEMBER – a Circuit is… An uninterrupted pathway or loop through which electricity can flow (usually wire pathway) Chapter 17 Electric Current and Electrical Energy Electric Current (I) Rate at which electrical charges (electrons) pass a given point; measured in amperes or amps (A) Chapter 17 Voltage (V) Also called Electric Potential Potential difference between two points in a circuit Measured in volts (V) A measure of how much work is needed to move a charge (current) between two points. Chapter 17 Voltage & Current As long as there is a voltage between two points on a wire, charges will flow in the wire. The size of the current depends on the voltage. The greater the voltage is, the greater the current is. A greater current means that more charges move in the wire each second. Chapter 17 Chapter 17 Voltage (V) Think of voltage as the amount of energy released as a charge moves between two points in the path of a current. The higher the voltage is, the more energy is released per charge Chapter 17 Resistance (R) Oposition to the amount of current in a wire OR “electric friction” Measured in ohms(Ω) Chapter 17 Resistance (R) Depends on: a) Type of material b) Thickness and length of wire c) Temperature Chapter 17 Resistance (R) The resistance of a short, thick piece of wire is less than the resistance of a long, thin piece of wire. Chapter 17 Resistance (R) Resistance & Temperature In general, the resistance of metals increases as temperature rises. Superconductors If you cool certain materials to a very low temperature, resistance will drop to 0 Ω. Materials in this state are called superconductors Superconductors One interesting property of superconductors is that they repel magnets. The superconductor in this photo is repelling the magnet so strongly that the magnet is floating. Chapter 17, HOLT textbook Chapter 17 Household Circuit Safety • Circuit Failure Broken wires or water can cause a short circuit. In a short circuit, charges do not go through one or more loads in the circuit. • Fuses A fuse has a thin strip of metal. Fuses keep charges from flowing if the current is too high. Chapter 17 Household Circuit Safety, con’t • Circuit Breakers A circuit breaker is a switch that automatically opens if the current is too high. Charges stop flowing. • Electrical Safety Tips Do not overload circuits by plugging in too many electrical devices. Do not use electrical devices near water.