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Electricity

Electricity. Physical Science Chapter 17. Electric charge. Neutral Equal positive and negative charges Positive Fewer negative charges (lost electrons) Negative More negative charges (gained electrons). Static electricity. The accumulation of electric charges on an object. Charges.

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Electricity

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  1. Electricity Physical Science Chapter 17 Physical Science chapter 17

  2. Electric charge • Neutral • Equal positive and negative charges • Positive • Fewer negative charges (lost electrons) • Negative • More negative charges (gained electrons) Physical Science chapter 17

  3. Static electricity • The accumulation of electric charges on an object. Physical Science chapter 17

  4. Charges • Like charges repel • Opposite charges attract Physical Science chapter 17

  5. Charging by contact • A charged object touching an uncharged object causes electrons move around until they are evenly spread throughout both objects. • When the charged object is removed, the other object has a charge • See page 589 Physical Science chapter 17

  6. Charging by induction • A charged object causes the electrons on a neutral object to rearrange themselves. • The charged object and the neutral object are then attracted to each other. • See page 588 Physical Science chapter 17

  7. Conductor • Material that allows electrons to move easily through it • metals Physical Science chapter 17

  8. Insulator • A material that doesn’t allow electrons to move through it easily • Plastic • Wood • Rubber • Glass Physical Science chapter 17

  9. Discuss • What is static electricity? • What is the difference between a conductor and an insulator? Physical Science chapter 17

  10. Electric force • Push (repulsion) or pull (attraction) experienced by charged particles. • Depends on charge and distance • Larger charges make larger forces • Smaller distances make larger forces Physical Science chapter 17

  11. Electric field • How a charged particle exerts a force on other particles. • The field is strongest closest to the particle. • Field lines point in the direction of the force on a positive charge. • Field lines never cross Physical Science chapter 17

  12. discuss • What is an electric field? Physical Science chapter 17

  13. Electrical Potential Energy • Energy an electric charge has based on its position in an electric field Physical Science chapter 17

  14. Moving electrons • Electrons move from areas of high potential energy to areas of low potential energy • When the potential energies are equal, the electrons stop Physical Science chapter 17

  15. Potential Difference • Potential energy change divided by charge • Measured in volts (V) • Often called voltage Physical Science chapter 17

  16. Electric Current • The flow of electrons through a conductor • Amount of current depends on number of electrons passing a point in a given time. • Measured in amperes or amps (A) • 1 ampere is 1 coulomb of charge per second • 1 coulomb is the charge of 6.24 x 1018 electrons Physical Science chapter 17

  17. Batteries • Made of electrochemical cells • Have a potential difference between the positive and negative terminals • Electrons are released in a chemical reaction • As long as the reaction occurs, the battery works. • Dry cell batteries contain a pastelike electrolyte • Wet cell batteries contain a liquid electrolyte Physical Science chapter 17

  18. Resistance • The tendency of a material to resist electron flow • Measured in ohms (W) • Conductors have low resistance. • Insulators have high resistance. Physical Science chapter 17

  19. Ohm’s Law • The current in a circuit depends on both voltage and resistance Physical Science chapter 17

  20. Example • Find the current flowing through a wire if its resistance is 20 W and it is connected to a 12-V battery. Physical Science chapter 17

  21. You try • Find the current flowing through a wire if its resistance is 20 W and it is connected to a 6-V battery. Physical Science chapter 17

  22. Semiconductors • Conduct electricity under certain conditions • In pure state – insulators • With carefully added impurities – conductors • Used in electronics Physical Science chapter 17

  23. Discuss • What is current? • What is resistance? • What three quantities are related by Ohm’s law? Physical Science chapter 17

  24. Circuit • A closed path for electrons • Electrons continue to flow as long as there is a potential difference • Common source is a battery Physical Science chapter 17

  25. Schematic diagrams • Used to show the construction of a circuit • Symbols used shown on page 602 Physical Science chapter 17

  26. Series circuits • The current only has one possible path. • The current is the same everywhere. • If one part goes out, the circuit is broken and it won’t work. Physical Science chapter 17

  27. Parallel Circuits • Contain separate branches for current to move through. • The current is different in each branch. • More current goes through branches with less resistance. • The potential difference is the same in each branch. • When one branch is opened, the current continues to flow through the other branches Physical Science chapter 17

  28. Discuss • Section 3 Review #1 on page 607 Physical Science chapter 17

  29. Power • The rate at which work is done – chapter 13 • Electrical power – the rate at which electrical energy is converted to another form of energy Physical Science chapter 17

  30. Power • Expressed in watts (W) or kilowatts (kW) • Found by multiplying current times voltage. Physical Science chapter 17

  31. Example • A lamp operates with a current of 0.625 A and a potential difference of 120 V. How much power does it use? Physical Science chapter 17

  32. You try • A microwave oven uses 1000 W of power. The voltage source is 120 V. What is the current flowing through the microwave? Physical Science chapter 17

  33. You try • The current in the heating element of an iron is 5.0 A. If the iron dissipates 590 W of power, what is the voltage across the iron? Physical Science chapter 17

  34. You try • A single solar panel for home use puts out 550 W of electrical power. If the electrical current produced by this panel is 4.2 A, calculate the voltage generated by the panel. Physical Science chapter 17

  35. Household circuits • Mostly parallel circuits. • Overheating protection is needed. • Fuses • Contain small pieces of metal that melt when the current gets too high • Must be replaced when blown • Circuit breakers • Contain metal that bends when the current gets too high • Can be reset by flipping a switch Physical Science chapter 17

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