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Chapter 17 BRAINSTORMING •On a clean journal page write today’s date and the title … “BRAINSTORMING” Now write/draw as many facts about electricity as you can. You have 3-4 minutes only Chapter 17 WARM-UP 2/10/2012 1. Get your journals and have a seat 2. Please complete the Phase Change Review Paper Warm – Up Phase Change Graph Review Chapter 17 WARM-UP 2/13/2012 1. Get your journals and have a seat 2. We will be taking a Pre-Quiz today 3. Tape the reading passage into your journal Student Led Demo “Snap, Crackle, Jump” 2/13/2012 Vinyl Albums are “old fashioned” form of popular music. Watch what happens when I rub the vinyl and then hold it over the rice krispies… Chapter 17 Student Investigation “Rub a Balloon” 2/13/2012 1. Each group has an investigation kit at their table 2. Each student is responsible for completing their own lab sheet Chapter 17 Warm-Up 2/14/2012 1. You will need your journal 2. Complete Warm Up Worksheet ***Activities #25-#26*** 3. Tape into your journal Chapter 17 Warm-Up 2/15/2012 3-2-1 In your journal’s write down: 3 Things you learned from yesterday 2 Question’s you have 1 Guess at what we will be doing today! 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 ESSENTIAL QUESTION What is electrical energy? Chapter 17 Electric Charge Charges Exert Force Atoms are composed of particles with electric charge. The law of electric charges states that like charges repel and opposite charges attract. Chapter 17 Matter Review Matter is made up of small particles called atoms. Chapter 17 Electric Charge Protons have a positive charge Electric charge is a property that allows an object to exert a force another object without touching it. The Force Between Protons and Electrons Because protons and electrons have opposite charges, they are attracted to each other. Electrons have a negative charge Electric Force The force between charged objects is an electric force. It is the force (a push or a pull) on a charged object due to an electric field Note: Like charges push Unlike charges pull Electric Field •An Electric Field is the region around a charged object in which another charged object experiences an electric force Law of Electric charges Like charges will repel (push away) each other and unlike charges will attract (pull toward) one another Law of Electric charges The force (a push or a pull) on a charged object due to an electric field Note: Like charges push Unlike charges pull Chapter 17 Chapter 17 Remember… Most objects have approximately the same number of protons and electron. They have no electrical charge. They are neutral Chapter 17 So How do Objects Become Charged? Objects can become charged when electrons are transferred by: 1. Conduction 2. Induction 3. Friction Chapter 17 Charge It! • Friction Charging by friction happens when electrons are “wiped” from one object onto another. Chapter 17 Charge It! •Conduction Charging by conduction happens when electrons move from one object to another by direct contact. Chapter 17 Remember… Like thermal energy, which flows from more energy to less, electric energy will flow from area that has more charges to an area with less charges. Charge will move until equilibrium is reached. Chapter 17 Charge It! Induction - movement of electrons to one part of an object because of the influence of the electric field of another object Charges can move between two objects that are touching Chapter 17 Charge It! When a charge object is brought nearby, one charge is attracted to the object and the other charge is repelled by the object. Chapter 17 Charge It! The two objects are separated while the charged rod is still nearby. Now apart, charges can no longer move from one object to the other. Chapter 17 Charge It! Charged object is removed from the area. Two objects are now oppositely charged. What would happen if the two object were moved so they were touching again? Charge It!, continued Static Electricity Electrical charge at rest on an object Electrical Discharge The release of electricity stored in an object Key Concept… When a negatively charged object comes close to a positively charged object, electrons move to neutralize the charge Key Concept Continued Key Idea continued If a neutral state (charge of zero) can not be reached, electrons will move until the number of excess electrons or protons is the same on both objects. Familiar Static… Lightning – positive charges collect at the top of a cloud; Negative charges collect at the bottom of the cloud . Chapter 17 Lightning Danger!!! Lightning Dangers It is particularly dangerous to be at the beach or on a golf course during a lightning storm. Even standing under a tree during a storm is dangerous. Thunderstorm clouds’ negative charges are usually attracted to the highest nearby positive object – YOU! Chapter 17 Lightning Rods A lightning rod is a pointed rod connected to the ground by a wire. Objects that are joined to Earth by a conductor, such as a wire, are grounded. Chapter 17 Detecting Charge You can use a device called an electroscope to see if something is charged. Chapter 17 Moving Charges Conductors An electrical conductor is a material in which charges can move easily. Insulators An electrical insulator is a material in which charges cannot move easily. Chapter 17 Electric Current • Electric current is the rate at which charges pass through a given point. Electric current is expressed in units called amperes, or amps. • Making Charges Move When you flip a switch, an electric field is set up in the wire at the speed of light. The electric field causes the free electrons in the wire to move. Chapter 17 Electric Current, continued • Commanding Electrons to Move This electric field is created so quickly that all electrons start moving through the wire at the same instant. Think of the electric field as a command to the electrons to charge ahead. Chapter 17 Electric Current, continued • AC and DC There are two kinds of electric current—direct current (DC) and alternating current (AC). Chapter 17 Voltage • Voltage is the potential difference between two points in a circuit. Voltage is expressed in volts (V). • Voltage and Energy Voltage is a measure of how much work is needed to move a charge between two points. You can think of voltage as the amount of energy released as a charge moves between two points in the path of a current. Chapter 17 Electric Current and Electrical Energy Voltage, continued • Voltage and Electric 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. • Varying Nature of Voltage Different devices need different levels of voltage. Chapter 17 Resistance • Resistance is the opposition to the flow of electric charge. • Resistance and Material Good conductors, such as copper, have low resistance. Poor conductors, such as iron, have higher resistance. • Resistance, Thickness, and Length Thick, short wires have less resistance than thin, long wires. Chapter 17 Resistance, continued • Resistance and Temperature In general, the resistance of metals increases as temperature rises. Chapter 17 Generating Electrical Energy • Parts of a Cell A cell contains a mixture of chemicals called an electrolyte. Every cell also has a pair of electrodes made from conducting materials. • Kinds of Cells Two kinds of cells are wet cells and dry cells. The electrolytes in dry cells are solid or pastelike. Chapter 17 Chapter 17 Generating Electrical Energy, continued • Thermocouples Thermal energy can be converted into electrical energy by a thermocouple. • Photocells A photocell converts light energy into electrical energy. Chapter 17 Connecting Current, Voltage, and Resistance • Georg Ohm (1789 –1854) studied the resistances of materials. He measured the current that resulted from different voltages applied to a piece of metal wire. • Ohm’s Law Ohm found that the ratio of voltage to current is a constant for each material. This ratio is the resistance of the material. Chapter 17 Connecting Current, Voltage, and Resistance, continued Chapter 17 Chapter 17 Electric Power • What Is Electric Power? The rate at which electrical energy is changed into other forms of energy is electric power. Electric power is calculated using the following equation: power voltage current, or P V I • Watt: The Unit of Power The unit for power is the watt (W). Another common unit of power is the kilowatt (kW). One kilowatt is equal to 1,000 W. Chapter 17 Electric Power, continued • Power Ratings When you read the wattage label on a light bulb, you are reading the bulb’s power rating. The power rating describes the rate at which an electric device uses electrical energy. Chapter 17 Measuring Electrical Energy • The amount of electrical energy used in a home depends the power of the electrical devices in the house and the length of the time that those devices are on. The equation for electrical energy is as follows: electrical energy power time, or E P t Chapter 17 Chapter 17 Measuring Electrical Energy, continued • Measuring Household Energy Use Different amounts of electrical energy are used each day in a home. Electric companies usually calculate electrical energy by multiplying the power in kilowatts by the time in hours. • How to Save Energy Every appliance uses energy. Replacing items that have high power ratings with items that have lower ratings is a way to save energy. Chapter 17 Measuring Electrical Energy, continued • It’s All About the Bulb All of the lighting in a home could make up as much as 25% of a home’s energy consumption. So, buying and using energy–efficient light bulbs can make a big difference in the amount of energy used by a household. • Energy–Saving Programs Many governments and organizations around the world have started programs to help save energy and natural resources. Chapter 17 Parts of an Electric Circuit • Forming a Loop An electric circuit is a complete, closed path through which electric charges flow. • All circuits need three basic parts: an energy source, wires, and a load. Chapter 17 Section 4 Electric Circuits Chapter 17 Section 4 Electric Circuits Parts of an Electric Circuit, continued • A Switch to Control a Circuit Sometimes, a circuit also contains a switch. A switch is used to open and close a circuit. Chapter 17 Section 4 Electric Circuits 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 Section 4 Electric Circuits Types of Circuits, continued • 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. Chapter 17 Section 4 Electric Circuits 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 Section 4 Electric Circuits Household Circuit Safety, continued • 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.