Chapter 7 Physical science


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Chapter 7 Physical science

  1. 1. Chapter 7 Electricity
  2. 2. Structure of Atoms Atoms contain the following… Location Charge Particle Outside the nucleus -1 Electron Nucleus 0 Neutron Nucleus +1 Proton
  3. 3. Positive and Negative Charges <ul><li>In most atoms, the negative charge cancels out the positive charge. These atoms are said to be electrically neutral . </li></ul>
  4. 4. Static Electricity <ul><li>The accumulation of excess electrical charge on an object. </li></ul><ul><li>Ex: </li></ul><ul><li>Walking on carpet. Electrons are transferred from the carpet to your shoes. </li></ul><ul><li>Lightning is a very large static charge </li></ul>
  5. 5. Charges Exert Forces <ul><li>The force on the atoms depends on… </li></ul><ul><li>The distance between the atoms. </li></ul><ul><li>The amount of charge on the atoms. </li></ul>Opposite charges attract Like charges repel
  6. 6. <ul><li>An electric field surrounds every electric charge and exerts the force that causes other electric charges to be attracted or repelled. </li></ul><ul><li>Any charge that is placed in an electric field will be pushed or pulled by the field. </li></ul>Electric Fields
  7. 7. Electrical Fields
  8. 8. Northern Lights
  9. 9. Earth’s Electric Field
  10. 10. Law of Conservation of Charge <ul><li>A charge can be transferred from object to object, but cannot be created or destroyed. </li></ul>
  11. 11. Static Charge
  12. 12. Charging Objects By Contact <ul><li>Charges can be transferred by rubbing or touching objects. </li></ul><ul><li>Ex: Rubbing your shoes on carpet or rubbing your hair with a balloon. </li></ul>
  13. 13. Charging By Induction (Charging at a distance) <ul><li>Charged objects brought near a neutral object will cause electrons to rearrange their positions on the neutral object. </li></ul>
  14. 14. Charging at a Distance <ul><li>The balloon on the left is electrically neutral. </li></ul><ul><li>The balloon on the right is negatively charged and produces a positively charged area on the sleeve by repelling electrons. </li></ul>
  15. 15. <ul><li>Lightning is a large static discharge. </li></ul>Lightning <ul><li>A static discharge is a transfer of charge between two objects because of a buildup of static electricity. </li></ul><ul><li>A thundercloud is a mighty generator of static electricity. As air masses move and swirl in the cloud, areas of positive and negative charge build up. </li></ul>
  16. 16. <ul><li>Eventually, enough charge builds up to cause a static discharge between the cloud and the ground. </li></ul>Lightning <ul><li>As the electric charges move through the air, they collide with atoms and molecules. These collisions cause the atoms and molecules in air to emit light . </li></ul>
  17. 17. Thunder <ul><li>Lightning also generates powerful sound waves. </li></ul><ul><li>The electrical energy in a lightning bolt rips electrons off atoms in the atmosphere and produces great amounts of heat. </li></ul><ul><li>The heat causes air in the bolt's path to expand rapidly, producing sound waves that you hear as thunder. </li></ul>
  18. 18. Grounding <ul><li>Connecting an object to Earth. </li></ul><ul><li>Providing a path for a charge to reach the Earth prevents an excess charge from building up. </li></ul>
  19. 19. Electroscope <ul><li>A device used to detect an electric charge. </li></ul>
  20. 20. Electric Current <ul><li>The net movement of electrons in a single direction. </li></ul><ul><li>Flows from higher voltage to lower voltage. </li></ul><ul><li>Measured in Amperes. (amps) </li></ul>
  21. 21. Voltage Difference <ul><li>The differences in electrical charges . </li></ul><ul><li>Measured in Volts . </li></ul>
  22. 22. Circuits <ul><li>A closed path that the electric current follows. </li></ul><ul><li>2-Types </li></ul>
  23. 23. Series Circuit <ul><li>Have only one loop to flow through. </li></ul><ul><li>EX: flashlights, some holiday lights. </li></ul>
  24. 24. Parallel Circuits <ul><li>Contain two or more branches for the current to move through. </li></ul><ul><li>The current can flow through both or either of the branches. </li></ul><ul><li>Advantage: When one branch opens the current continues to flow through the other branches. </li></ul>
  25. 25. Household Circuits <ul><li>A combination of parallel circuits connected in a network. </li></ul>
  26. 26. Protection From Overheating <ul><li>Fuses : Contain a small piece of metal that melts when it becomes overheated, breaking the circuit and stopping flow of current. </li></ul>
  27. 27. Circuit Breaker <ul><li>A circuit breaker contains a piece of metal that bends when the current in it is so large that it gets hot. </li></ul>
  28. 28. Electric Power <ul><li>The rate at which electrical energy is converted to another form of energy. </li></ul><ul><li>The unit for power is the watt (W). </li></ul><ul><li>(Often expressed in kilowatts (kW).) </li></ul>
  29. 29. Electric Power Continued… <ul><li>Use the equation below to calculate electrical power. </li></ul>
  30. 30. Electrical Energy Equation <ul><li>Use the following equation to calculate electrical energy. </li></ul>