Current Electricity


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Current Electricity

  1. 1. Current Electricity
  2. 2. Current Electricity <ul><li>Electricity is an important aspect of our daily lives </li></ul><ul><li>Most appliances use electricity that flows through conducting wires in the walls of our homes </li></ul>
  3. 3. Static vs. Current <ul><li>Electrons are always moving </li></ul><ul><li>In static electricity, the electrons gather in one place and move randomly in all directions </li></ul>
  4. 4. Static vs. Current <ul><li>In current electricity, there is a steady flow of electric charge (electrons) through a conductor </li></ul>
  5. 5. Static vs. Current <ul><li>With static electricity, charges flow between two objects during an electrostatic discharge </li></ul><ul><li>However, these charges follow an unpredictable path and it occurs for only a very short period of time </li></ul>
  6. 6. Static vs. Current <ul><li>In current electricity, the charges move steadily for a much longer period of time </li></ul><ul><li>This steady flow can be controlled and used to power various electrical devices </li></ul>
  7. 7. Conductors & Insulators <ul><li>Recall that electrons move easily through conductors </li></ul><ul><li>Human skin is a fair conductor, therefore it is very dangerous to touch a conducting wire that has electricity moving through it </li></ul>
  8. 8. Conductors & Insulators <ul><li>For safety, conducting wires are wrapped with an insulator , such as plastic, which prevents the flow of electrons from entering your body . </li></ul>
  9. 9. Making Electrons Move <ul><li>What makes electrons flow in a conductor? </li></ul>Consider an mp3 player and a computer monitor…
  10. 10. Making Electrons Move <ul><li>A fully charged battery is needed to operate the mp3 player. </li></ul><ul><li>If the battery is charged, electrons can flow through the mp3 player and it works </li></ul>
  11. 11. Making Electrons Move <ul><li>If the battery is dead, the electrons do not flow and the mp3 player does not work </li></ul>
  12. 12. Making Electrons Move <ul><li>Not all devices require a battery to create the flow of electrons </li></ul><ul><li>A computer monitor, for example, is usually plugged into a wall outlet </li></ul>
  13. 13. Making Electrons Move <ul><li>In this case, the flow of electrons is produced by an electric generating station </li></ul><ul><li>The electrons eventually flow into the wires in your home and then into your monitor </li></ul>
  14. 14. <ul><li>If there is a blackout, electrons do not flow and the monitor does not work </li></ul><ul><li>No matter what the electrical device is, to make it operate you need a source of electrical energy </li></ul>
  15. 15. Electrochemical Cells <ul><li>One simple and convenient energy source is a battery </li></ul><ul><li>A battery is a combination of electrochemical cells </li></ul><ul><li>Each electrochemical cell is a package of chemicals that converts chemical energy into electrical energy </li></ul>
  16. 16. Electrochemical Cells <ul><li>A simple electrochemical cell includes an electrolyte and two electrodes </li></ul><ul><li>An electrolyte is a liquid or paste that conducts electricity because it contains chemicals that form ions </li></ul>
  17. 17. Electrochemical Cells <ul><li>Electrodes are metal strips that react with the electrolyte </li></ul><ul><li>Two different electrodes, such as zinc and copper , are used in a battery </li></ul>
  18. 18. Electrochemical Cells <ul><li>The electrolyte reacts with the electrodes </li></ul><ul><li>One of the electrodes collects electrons, making it negatively charged </li></ul><ul><li>The other electrode loses electrons, making it positively charged </li></ul>
  19. 19. Wet Cells vs. Dry Cells <ul><li>An electrochemical cell that has a liquid electrolyte is called a wet cell </li></ul><ul><li>Wet cells are often used as an energy source for cars and other motorized vehicles </li></ul>
  20. 20. Wet Cells vs. Dry Cells <ul><li>An electrochemical cell that uses a paste instead of a liquid electrolyte is called a dry cell </li></ul><ul><li>Dry cells are used in flashlights, hand-held video games, cameras and watches </li></ul>
  21. 21. Wet Cells vs. Dry Cells <ul><li>Each electrode in a dry cell or battery can also be called a terminal </li></ul><ul><li>Terminals are the end points in a cell or battery where we make a connection </li></ul>
  22. 22. Fuel Cells <ul><li>A fuel cell is an electrochemical cell that generates electricity directly from a chemical reaction with a fuel, such as hydrogen </li></ul>
  23. 23. Fuel Cells <ul><li>Fuel cells are not used up like an ordinary cell because as electricity is produced more fuel is added </li></ul><ul><li>Fuel cells are used in electric vehicles and may one day be used in smaller devices such as laptop computers </li></ul>
  24. 24. Potential Energy <ul><li>Each electron has electric potential energy </li></ul><ul><li>Potential energy is the energy stored in an object </li></ul>
  25. 25. <ul><li>Picture an apple hanging from a low branch on an apple tree. </li></ul><ul><li>The apple has potential energy because of its position above the ground </li></ul>Potential Energy
  26. 26. <ul><li>If the apple falls down, it will convert its stored energy, or potential energy, into motion </li></ul>Potential Energy
  27. 27. <ul><li>Suppose the apple were on a higher branch. </li></ul><ul><li>It would have even more potential energy to convert… </li></ul>Potential Energy
  28. 28. <ul><li>The greater the height of an apple above the ground, the greater its potential energy . </li></ul>Potential Energy
  29. 29. <ul><li>A battery has chemical potential energy in the electrolyte in its electrochemical cells. </li></ul>Potential Energy
  30. 30. <ul><li>The chemicals in the electrolyte react with the electrodes, causing a difference in the amount of electrons between the two terminals </li></ul>Potential Energy
  31. 31. <ul><li>One terminal in a battery has mainly negative charges (electrons) </li></ul><ul><li>The other terminal has mainly positive charges. </li></ul><ul><li>The negative charges are electrons , which can move </li></ul>Potential Energy
  32. 32. <ul><li>The electrons from the negative terminal are attracted to the positive charges at the positive terminal </li></ul><ul><li>If the two terminals are connected using a conductor, then electrons flow from the negative terminal to the positive terminal </li></ul>Potential Energy
  33. 33. Potential Energy
  34. 34. <ul><li>The difference in electric potential energy between two points in a circuit is called the potential difference or voltage </li></ul><ul><li>This difference is what causes current to flow in a closed circuit </li></ul>Potential Energy
  35. 35. <ul><li>The higher the potential difference in a circuit, the greater the potential energy of each electron </li></ul>Potential Energy
  36. 36. <ul><li>The potential difference between two locations in a circuit is measured with a voltmeter . </li></ul><ul><li>The unit for measuring potential difference is the volt (V) </li></ul>Potential Energy
  37. 37. <ul><li>Electric current is a measure of the amount of electric charge that passes by a point in an electrical circuit each second </li></ul>Current
  38. 38. <ul><li>The flow of current from batteries is called direct current (DC) because the current flows in only one direction (negative to positive) </li></ul>Current
  39. 39. <ul><li>The current that flows through cords plugged into wall sockets is called alternating current (AC) </li></ul>Current
  40. 40. <ul><li>Alternating current flows back and forth at regular intervals called cycles . </li></ul><ul><li>This is the current that comes </li></ul><ul><li>from generators </li></ul><ul><li>and is carried </li></ul><ul><li>by power lines </li></ul><ul><li>to your home </li></ul>Current
  41. 41. <ul><li>The flow of current in a circuit is measured using an ammeter . </li></ul><ul><li>The unit for electric current is the ampere (A) </li></ul>Current
  42. 42. <ul><li>Resistance is the degree to which a substance opposes the flow of electric current through it </li></ul>Resistance
  43. 43. <ul><li>Conductors , such as metals, allow electrons to flow freely through them and have low resistance values. </li></ul>Resistance
  44. 44. <ul><li>Insulators resist electron flow greatly and have high resistance values. </li></ul>Resistance
  45. 45. <ul><li>Resistance is measured in ohms (  ) using an ohmmeter </li></ul>Resistance
  46. 46. <ul><li>Any material that can slow current flow is called a resistor . </li></ul><ul><li>For example, the resistance in the filament of a light bulb causes it to heat up and produce light </li></ul>Resistance
  47. 47. <ul><li>The shorter and thicker a wire, the less resistance it creates for electrons </li></ul><ul><li>Other factors affecting the resistance of a wire include the material it is made from and its temperature </li></ul>Resistance
  48. 48. Wider wires offer less resistance than thinner wires. If the wire doubles in width, its resistance is half as great. Conducting wires that carry large currents need large diameters to lessen their resistance. Diameter Longer wires offer more resistance than shorter wires. If the wire doubles in length, it doubles in resistance. Length As the temperature of the wire increases, its resistance increases and its conductivity decreases. In other words, a colder wire is less resistant than a warmer wire. Temperature Silver has the least resistance but is very expensive to use in wires. Most conducting wires are made from copper. Material How Factor Affects Resistance Factor