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Transcript
ELECTRICITY SYMBOLS • We have looked at several different symbols • We will be using many of them from now on so get used to them Conductors • Materials that allow electricity to flow easily thru it – Material made up of atoms with the valance ring (outer) with 1, 2, or 3 electrons • Most metals Insulators • Materials that don’t’ allow electricity to flow easily thru it – Material made up of atoms with the valance ring with 5, 6, 7, or 8 electrons • • • • Air Glass Paper Wood Semi Conductors • Materials that are not good conductors or good insulators – Material made up of atoms with the valance ring with 4 electrons • Carbon (C) • Silicon (Si) Electricity • The flow of electrons – How do we get electrons to flow? Electrons being held In orbit by the attraction Of the protons Two copper atoms side by side Two copper atoms side by side Copper wire Made up of billions of copper atoms Electrons bouncing around in random drift in the wire Remember the wire is full of electrons at Random drift. Atoms loosing or gaining electrons • All atoms have an equal number of protons and electrons • When an atom looses one electron it becomes a Positive Ion – It is now unstable and wants an electron back to become stable • When an atom gains an electron it becomes a Negative Ion – It is now unstable and wants to get rid of an electron to become stable Shortage of electrons here Extra Electrons here Now the electrons that were at random drift are in a directed drift Voltage • Electrical pressure (pushes current) Atoms that are short electrons and atoms with extra electrons Unit of measure is the volt Measured with a voltmeter Note! A good voltmeter won’t have any flow thru it Ways to make voltage • • • • • • Magnets Chemical Pressure Heat Light Friction Most common Current • The directed movement of electrons or the flow. (pushed by voltage) Unit of measure is the amp or ampere Measured with an ammeter or amp meter How much is one amp? • One amp is 6.25 X 10 to the 18th power of electrons past a given point per second. (one Coulomb) 6,250,000,000,000,000,000 Conventional theory Says that current flows from + to Scientists first guessed that it was the proton that was in motion in the atom Electron theory Says that current flows from – to + When scientists discovered that it was the electron that was in motion, electron theory was born Does it matter? • When talking about electronics, it does matter which way current flows, but for basic electricity, it doesn’t • Most automotive texts, and classes still teach conventional theory, so that is what we will stick with. Resistance • Opposition to current flow (anything that slows down current) Unit of measure is the ohm Measured with an ohmmeter Factors that affect the resistance of a circuit • Type of material used – Conductor / Insulator / Semi-conductor • • • • Length of the circuit Diameter of the circuit Temperature Connections Wire diameter • AWG Gauge size • American Wire Gauge • Metric – Millimeters squared 36 0.005 0000 0.500 Elements of a Circuit (must have) Nice to have One wire circuits OHM’S LAW • When the voltage and resistance are equal in a circuit, ONE amp will flow (Saunders version) • One volt will push one amp through one ohm of resistance A picture is worth a thousand words Ohms Law • Current flow is strictly a result of how much voltage and resistance there is – To get more current • Increase voltage • Decrease resistance • Or both – To get less current to flow • Decrease voltage • Increase resistance • Or both Ohm’s law formulas • Voltage is represented by the letter “E” • Amperage is represented by “I” • Resistance is represented by “R” E=IxR Here is an easier way to remember The three formulas Need to know When you know the amperage and resistance of a circuit you can figure the voltage Voltage = amperage times resistance When you know the voltage and amperage of a circuit you can figure the resistance Resistance = voltage divided by amperage When you know the voltage and resistance of a circuit you can figure the amperage Amperage = voltage divided by resistance D.C Challenge • Let’s apply what we have learned – Ohms law • We will also learn about electrical power or watts – Power is the rate of doing _________ – Watts are the amount of electrical work • There will be an ohm’s law and power quiz after D.C. Challenge ELECTRICITY After ATECH 1-7 Series Circuit Rules Must know! • Only one path • Amperage stays the same • Each resistance adds up to the total • R1+R2=Rt • Voltage divided between the loads (all used up or dropped) Voltmeters • Hooked across or in parallel – Red to most positive and black to most negative – Used in a live circuit Ammeters • Hooked in series (in line and part of the circuit) – Red to most positive and black to most negative – Used in a live circuit Be careful not to hook across voltage (it will blow fuse Ohm Meters • Used in a dead circuit • Must be hooked across or in parallel • Analog meter must be calibrated to compensate for battery • Part you want to measure must be isolated from the rest of the circuit • Good connections Atech 8-11 Type of circuits Atech 12-14 Atech 1-7 ATECH 7-11 • Parallel circuits – The rules are going to change Lets go get it done! ELECTRICITY Problem Circuits • • • • Open Circuit No flow Infinite resistance Won’t use circuit protection Meters to find open – Volt (will read source voltage across open) – Ohm (will read infinite across open) High resistance • Less flow than normal • Won’t use circuit protection • Meters to find – Voltmeter (will drop more voltage at problem) – Ohmmeter (will read more resistance at problem) Short circuit • More flow than normal • May use circuit protection • Meters to use – Ohmmeter (less resistance at problem) – Voltmeter (only if circuit is still live, voltmeter will read less voltage drop at problem) Grounded circuit (short to ground, dead short) • Huge flow (no resistance) • Will use circuit protection or burn up circuit • Ohmmeter is the only meter to use (circuit will be dead) – Ohmmeter will show no resistance to ground at the problem Short to voltage • Hardest to find and fix • When one circuit shorts voltage into another Low voltage • Won’t use circuit protection • Less amps will flow • Caused by – Bad battery – Charging system fault Circuit Protection D.C. Current • Current always flowing the same way A.C. Current • Current flows first one way, then the other Type of circuits