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5.1 static


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5.1 static

  1. 1. 5.1 Static 9 January 2011 Have you ever received a static electric shock? Where? What caused it?
  2. 2. What do the following pictures have in common?
  3. 3. Aims Show that when insulating objects are rubbed together they become charged Explain that there are repulsive forces between objects with similar charge and attractive forces with opposite charges State that a flow of charge is a current
  4. 4. Triboelectric effect (charging by rubbing)
  5. 5. Charges and electrostatics
  6. 6. Rub an acetate rod with a cloth. cloth acetate rod
  7. 7. After it has been rubbed, the rod has a positive charge, and the cloth has a negative charge. A possible explanation is that some electrons have been transferred from the cloth to the rod. both are charged
  8. 8. polythene rod polythene rod rubbed ends repel The ends of two polythene rods rubbed with a cloth will repel each other.
  9. 9. If one polythene rod is replaced with a rubbed acetate rod, the two ends will attract. polythene rod acetate rod rubbed ends attract
  10. 10. It can be shocking.
  11. 11. It can be annoying – or even dangerous.
  12. 12. It can be annoying – or even dangerous.
  13. 13. It can be annoying – or even dangerous.
  14. 14. It can be annoying – or even dangerous.
  15. 15. It can be useful.
  16. 16. It can be useful.
  17. 17. It can be useful.
  18. 18. It can be useful.
  19. 19. Charging by rubbing Electrical effects can be produced by rubbing two materials together When you rub a piece of plastic it is somehow changed, it can then effect objects at a distance. The plastic has been charged
  20. 20. Two types of charge If you rub identical plastic rods and then hold them close together, the rods push apart – they repel The forces they exert on each other are very small, so you can only see the effects if one of the rods are free to move If you do this with different plastic you find some pairs that attract each other The explanation is that there are two kinds of charge, we call this positive and negative
  21. 21. Where does this charge come from? Scientists believe that charge is not made but is moved around when two objects rub If you rub a plastic rob with a cloth, both the rod and the cloth become charged Each object gets a different charge; rubbing separates charge!