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ELECTRICITY - PowerPoint PPT Presentation

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  2. We have looked at several different symbols We will be using many of them from now on so get used to them SYMBOLS

  3. 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 Conductors

  4. 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 Insulators

  5. 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) Semi Conductors

  6. The flow of electrons How do we get electrons to flow? Electricity Electrons being held In orbit by the attraction Of the protons

  7. Two copper atoms side by side

  8. Two copper atoms side by side

  9. 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.

  10. 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 Atoms loosing or gaining electrons

  11. Shortage of electrons here Now the electrons that were at random drift are in a directed drift Extra Electrons here

  12. Electrical pressure (pushes current) Atoms that are short electrons and atoms with extra electrons Voltage • Unit of measure is the volt • Measured with a voltmeter Note!A good voltmeter won’t have any flow thru it

  13. Magnets Chemical Pressure Heat Light Friction Most common Ways to make voltage

  14. The directed movement of electrons or the flow. (pushed by voltage) Current • Unit of measure is the amp or ampere • Measured with an ammeter or amp meter

  15. One amp is 6.25 X 10 to the 18th power of electrons past a given point per second. (one Coulomb) How much is one amp? 6,250,000,000,000,000,000

  16. Conventional theory Says that current flows from + to - Scientists first guessed that it was the proton that was in motion in the atom

  17. Electron theory Says that current flows from – to + When scientists discovered that it was the electron that was in motion, electron theory was born

  18. 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. Does it matter?

  19. Opposition to current flow (anything that slows down current) Resistance • Unit of measure is the ohm • Measured with an ohmmeter

  20. Type of material used Conductor / Insulator / Semi-conductor Length of the circuit Diameter of the circuit Temperature Connections Factors that affect the resistance of a circuit

  21. AWG Gauge size American Wire Gauge Metric Millimeters squared Wire diameter

  22. 0.005 36 0000 0.500

  23. Elements of a Circuit (must have) Nice to have

  24. One wire circuits

  25. 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 OHM’S LAW A picture is worth a thousand words

  26. 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 Ohms Law

  27. Voltage is represented by the letter “E” Amperage is represented by “I” Resistance is represented by “R” Ohm’s law formulas E = I x R

  28. Here is an easier way to remember The three formulas Need to know Need to know

  29. When you know the amperage and resistance of a circuit you can figure the voltage Voltage = amperage times resistance

  30. When you know the voltage and amperage of a circuit you can figure the resistance Resistance = voltage divided by amperage

  31. When you know the voltage and resistance of a circuit you can figure the amperage Amperage = voltage divided by resistance

  32. 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 D.C Challenge


  34. 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) Series Circuit Rules Must know!

  35. Hooked across or in parallel Red to most positive and black to most negative Used in a live circuit Voltmeters

  36. Hooked in series (in line and part of the circuit) Red to most positive and black to most negative Used in a live circuit Ammeters Be careful not to hook across voltage (it will blow fuse

  37. 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 Ohm Meters

  38. Atech 8-11 Atech 12-14 Type of circuits Atech 1-7

  39. Parallel circuits The rules are going to change ATECH 7-11

  40. Lets go get it done!


  42. Problem Circuits

  43. 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) Open Circuit

  44. 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) High resistance

  45. 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) Short circuit

  46. 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 Grounded circuit(short to ground, dead short)

  47. Hardest to find and fix When one circuit shorts voltage into another Short to voltage

  48. Won’t use circuit protection Less amps will flow Caused by Bad battery Charging system fault Low voltage