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Chapter 16:Electricity Section 1 What is Electricity? Slide 2 Definition: electricity energy transferred as protons or electrons flow. Electricity is caused by unbalanced electric charge. e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- Slide 3 Definition: electric charge - a property of matter based on the number of electrons on an object. Objects can gain or lose electrons to change their charge. Benjamin Franklin identified the property of electric charge and gave it the positive/negative name! Slide 4 Electric charge can be positive, negative, or neutral. Positive: more + than Negative: more than + Neutral: Same number of + and + + + ++ + + + + + + - - - - - - - - - - Slide 5 Some materials allow charges to flow, while other objects stop the flow of electrical charges. Definition: electrical conductor a material that allows charges to move freely. Definition electrical insulator a material that does not transfer charges easily. CONDUCTOR NSULATOR Slide 6 Some conductors: All Metals Salt Solutions (electrolytes) Silver is the best metal conductor! Some Insulators: Wood / Cloth Glass ; Plastic; Rubber; Air Insulators / Conductors Slide 7 Electric force is a property that is responsible for most of the common forces that we experience, like friction. Definition: electric force the attractive or repulsive force between objects due to their charge. Slide 8 Electric force exists as an invisible field around charged objects. It causes: Opposite charges attract. Like Charges repel. + - A positive electric field pushes outward. A negative electric field pulls inward. Slide 9 + - That explains why opposites attract! + + -- The arrows are pointing in the same direction Slide 10 Definition: static electricity a build up non-moving electric charges on an object. Static electricity is often produced by friction! Friction causes electrons to stick to some materials As more and more electrons build up, the static charge increases. Slide 11 Static discharge occurs when the static electricity flows away from its source. Static Electricity Slide 12 Definition: electric induction the process by which a charged object causes another object to become charged. Example: combing your hair causes static charge to form on the comb. The comb can then be used to charge pieces of paper. Slide 13 Chapter 16: Electricity Section 2 Electric Current Slide 14 When electrons begin moving, they form a stream of electricity, called a current. Definition: electrical current a measure of the # of electrons moving through a conductor. MORE ELECTRONS = MORE CURRENT Current is measured in amps (A). Slide 15 Electricity is often discussed in terms of voltage. Do you have any idea what voltage is? Definition: voltage the push that causes electric current to flow. Slide 16 Voltage measures the amount of work that must be done to move a charge. Voltage has units of volts, V. Yes, work has to be done to move electrons! The voltage on a battery, for instance, tells how much work that battery can do. Slide 17 Do you think a 1.5 volt battery can power a car? Of course not!! The car needs a 12 volt battery. The 1.5 v battery doesnt produce enough force to move all of the electrons needed to run the electronics. Electric Current Slide 18 Speaking of batteries Definition: battery a device able to convert chemical energy into electrical energy. Batteries DO NOT store electricity! So, how do batteries work? Each battery contains an electrolyte (an acid), a cathode, and an anode. Definition: cathode the + end of a battery. Definition: anode the - end of a battery. Slide 19 A neg. charge collects on the anode. The charge flows to the cathode when connected by a wire. Slide 20 Each of the batteries below have the SAME voltage, but are used in different electronics. What is different about them? THEY PUSH DIFFERENT AMOUNTS OF ELECTRONSWITH THE SAME AMOUNT OF FORCE. Slide 21 Its kinda like The water is moving at the same speed, but different amounts of water are being moved! The amount of water represents current (amps)in case you didnt figure that out yet. Moving a small amt. of water at 10 mph. Moving lots of water at at 10 mph. Think AAA batteryThink D-Cell battery Slide 22 When a current cannot flow through a material easily, it is encountering resistance. Definition: resistance opposition to the flow of electric current. In other words, resistance slows down or stops the flow of electrons. Electric insulators cause almost 100% resistance. Enough resistance to stop the flow of electricity. Slide 23 Resistance is a form of friction. Resistance can cause some electric energy to be converted into thermal energy Electric stoves work by using that fact! Electricity flows through The coil, which causes resistance. Electric Current Slide 24 Resistance is how incandescent light bulbs work. Why is knowing resistance important? Electricity travels through the wire coil and encounters resistance. The coil becomes hot from the resistance, and begins to glow. Inside the bulb, argon gas keeps the filament from catching on fire. Most filaments are made from the element Tungsten. Slide 25 LED bulbs and fluorescent bulbs do not require as much electric current as incan. bulbs. SoLEDs and Fluorescent bulbs are very energy efficient! Slide 26 Chapter 16:Electricity Section 3 Circuits Slide 27 When you flip the light switch, the light comes onobviously. What does the switch have to do with it?? The switch on the wall is part of a circuit. When it is switched to the ON position, it allows electric current to flow into the light bulb. What is a circuit? Slide 28 Whenever current flows, it encounters resistance. We can measure this resistance with: The Resistance Equation (Ohms Law): Resistance = Voltage/Current R = V/I Resistance is measured in Ohms (). Slide 29 Definition: circuit a set of components that allow one or more complete paths for electric current to flow. Any time electricity is flowing, a circuit is present. Circuits Slide 30 When electricity is able to flow freely through a circuit, that circuit closed. Incomplete circuits will not allow electricity to flow freely. They are called open circuits. Circuits Slide 31 Definition: series circuit a circuit that forms a single pathway. Electricity can only flow one way in a series circuit. Types of Circuits Slide 32 Definition: parallel circuit a circuit that forms multiple pathways for electricity. Parallel circuits can have a piece removed from them and still allow electricity to flow in another part of the circuit. Types of Circuits Slide 33 Slide 34 Slide 35 It is useful to know the resistance of objects in circuits. There are two rules used to calculate it: Series circuits have a total resistance of: R T = R 1 + R 2 +R 3 .. In other words, you add up the value of all the resistors. Parallel circuits have a total resistance of R T = 1/(R 1 + R 2 + R 3 ..) Thats all there is to it. Resistance in Circuits Slide 36 Circuits consist of many different things. The most common components of a circuit are: Power Supplies Wires Resistors Bulbs Switches Definition: resistor a device that blocks SOME (not all) electric current in a circuit. Appliances like TVs, lights, computersthese are all resistors. Circuit Components Slide 37 Electric resistance explains why electronics get hot as they run. Even conductors cause some resistance. As a wire gets thicker, there is less resistance. Electric Current in wires. Lots of ResistanceSome ResistanceLittle resistance Slide 38 As a wire gets shorter, there is less resistance. Electric Current in wires. Lots of ResistanceSome ResistanceLittle resistance Slide 39 As a wire gets thicker it can carry more electric current. Electric Current in wires. Slide 40 Basic Circuit Symbols (copy these to notes!) Resistor Wire Battery or Power Source Bulb Open Switch Closed Switch