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5. Comparing Electric and Gravitational Forces a. Electric force stronger than gravity b. All atoms are held together by electric forces greater than the gravitational forces between the same particles. If only there was a way to harness the E contained in atoms. Any ideas? c. Most objects are electrically neutral. No noticeable electric force. B. Conductors and Insulators 1. Conductors a. Material in which electrons are able to move about easily. b. Metals – atoms in metals have electrons that are able to move easily. Copper is the best. 2. Insulators a. A material in which electrons are not able to move easily. b. Electrons are held tightly. Plastic, wood, glass. C. Charging Objects a. Rubbing 2 materials together may result in a transfer of electrons. One is left with a positive charge and the other a negative. Charging by contact – sometimes called contact by friction. 1. Charging at a Distance a. Charging electrical forces act at a distance charged objects brought near a neutral will cause electrons to rearrange their positions on the neutral object. b. Charging by induction (not touching) – rearrangement of electrons on a neutral object caused by a nearby charged object. 2. Lightning a. Lightning is a large static charge. b. Cloud generates charges. As they swirl areas of positive and negative charges form. Eventually enough charge builds up to cause a discharge between the cloud and the ground. The collision between the charge and the atoms and molecules in the air cause light to emit. 3. Thunder a. Sound waves are also created. The electrical energy in lightning rips electrons off the atoms as it passes creating sound. 4. Grounding a. Electronics can be harmed by large static discharges. Grounding provides a path for the charges to go directly to the earth. Earth is neutral and a conductor. It will suck up charge. Lightning rods on top of tall buildings. D. Detecting Electric Charge a. Electroscope used to detect electric charge. Section Review – Vocab self-check ?s 2 and 3 Section 2 Electric Current A. Current and Voltage Difference a. Electric current – net movement of electric charges in a single direction. Usually in a wire. Slide for electric current. b. Measured in amperes. 1. Voltage Difference 1. Electron moving in current is similar to ball bouncing down stairs. 2. Flow of current is due to electric force. 3. Electric charge flows from high voltage to low voltage. 4. Voltage difference – the force that causes electric charges to flow. 5. Measured in volts. 2. Electric Circuits 1. Electric Circuit – closed path that electric current follows. B.Batteries a. Voltage difference needs to be maintained in circuit in order to keep electric current flowing. b. Current flows as long as there is 1. Closed path 2. Path connects one battery terminal to the other. 1. Dry Cell Batteries a. Cell consists of 2 electrodes surrounded by a material called an electrolyte. Electrolyte allows charges to move from electrode to electrode. b. Dry cell because electrolyte is moist paste not a liquid. 2. Wet Cell Batteries a. 2 connected plates made of different metals or metallic compounds in a conducting solution. b. Several wet cells connected together. 3. Lead-Acid Batteries a. Car batteries. b. 6 wet cells in a sulfuric acid solution. c. Chemical reaction that provides a voltage difference. d. Voltage difference at wall sockets. Usually higher than a battery. C. Resistance a. Filament – thin wire inside a light bulb. Electrons flow through filament they bump into metal atoms. b. This bumping causes some of the electrons to turn into thermal E. eventually there is enough thermal E for the filament to glow. It is this glow that lights the room (and Haleys smile) 1. Resisting the Flow of Current 1. Electric current loses E as it flows. The filament resists the flow of electrons. 2. Resistance – tendency for a material to oppose the flow of electrons, changing electrical E into thermal and light E. 3. Almost all materials have some electrical resistance. 4. Resistance is measured in ohms. 5. Copper has a low resistance. 2. Temperature length and thickness 1. Resistance increases with: 1. temperature. 2. length of wire. 3. thinness of wire. 4. Hallway example D. The Current in a Simple Circuit a. Contains 1. Voltage difference (battery) 2. Device (lightbulb) 3. Conductors (wires) b. When wires are connected to either end of the battery in a closed circuit current will flow. 1. Ohms Law 1. Relationship between voltage difference, current, and resistance is Ohms law. 2. Current in a circuit is equal to the voltage difference divided by resistance. Section Review – Vocab self-check 1,3 Section 3 Electrical E A. Series and Parallel Circuits a. Voltage difference – battery, outlet b. Devices that use E – lights, c. Conductors – wires that close circuit. 1. Series Circuits a. Only 1 loop for current to flow through. 2. open circuits a. Parts of a series circuit are wired one after another the amount of current is the same through every part. b. When any part is disconnected no current flows through the circuit. This is open circuit. Bad if you to play minecraft! 3. Parallel Circuits a. Parallel circuits contain 2 or more branches for the current to move though. b. All branches connect the same two points in circuit the voltage difference is the same in each branch. c. Advantages – if one path is opened current continues to flow through other branches. B.Household Circuits a. Wiring in house is parallel circuits. b. 120 volts coming out of standard American socket. c. Circuit breaker is electrical headquarters of your house. Parallel circuits originate here and flow electrons to other parts of your house. d. Distribute electricity to avoid making wires too hot. Heat will melt insulation and cause a fire. 1. Fuses a. Piece a metal that melts if circuit gets too hot. Once it melts the circuit is open and current stops. b. Before replacing the fuse unplug some items. c. Overheating is usually caused by too many appliances in the circuit. 2. Circuit Breaker a. A piece of metal than bends when overheated. Once it bends it flicks off the circuit to the off position. Once off no electrons are flowing. b. Before switching the circuit back on remove some appliances from the circuit. C. Electric Power a. Electric power – rate at which electrical E is converted to another form of E. b. We can convert electrical E into – light, heat, and mechanical E. c. Appliances that use heat (microwave/hair dryer) need more electrical E. 1. Calculating Electric Power a. Electric power depends on voltage difference and current. b. Unit for power is watt. Watt is small unit so power is often expressed as Kilowatts. 2. Electrical E a. Electric power costs money. Electric company charges by amount of electrical energy NOT electrical power. 3. Cost of Using Electrical E a. Cost of using an appliance can be calculated by multiplying the electrical E used by the amount the power company charges for each kilowatt. Section Review Vocab questions 1 - 2