Electricity

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Physics Ebbin Binny

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Electricity

  1. 1. Electricity Part I – Circuits
  2. 2. People Benjamin Franklin Thomas Edison  Have you heard of these people?  Why are they important?
  3. 3.  Benjamin Franklin Proved that lightning was electricity by flying a kite in a lightning storm Helped people understand the principles of electricity • Thomas Edison – Invented the electrical light bulb
  4. 4. What is electricity?  Electricity is a form of energy  It is caused by a flow of tiny particles called electrons through a material
  5. 5. Electricity Electricity is a flow of electric charges along a wire.
  6. 6. Electricity Electricity is a flow of electric charges along a wire.
  7. 7. Electricity Electricity is a flow of electric charges along a wire.
  8. 8. Electricity Electricity is a flow of electric charges along a wire.
  9. 9. Electricity Electricity is a flow of electric charges along a wire.
  10. 10. Electricity Electricity is a flow of electric charges along a wire.
  11. 11. Electricity Electricity is a flow of electric charges along a wire. This flow of electric charge is called a current. Current is measured in the units of Amps (A).
  12. 12. What is an Electrical Circuit?  A circuit is an electrical device that provides a path for electricity to flow
  13. 13. Complete or Incomplete?  A complete circuit is where all the components of a circuit are joined up and there are no gaps  The pathway for electricity is complete
  14. 14. Complete or Incomplete?  An incomplete circuit is where the pathway for electricity is broken  The electricity cannot flow
  15. 15. Circuit Diagrams cell switchlamp wires
  16. 16. Component Symbols – a cell  The cell stores chemical energy and transfers it to electrical energy when a circuit is connected.  The long line is the positive end  The short line is the negative end
  17. 17. Battery  When two or more cells are connected together we call this a Battery.  The cells chemical energy is used up pushing a current round a circuit.  It is important that each cell faces the right way
  18. 18. Switch  A switch can be open (as shown) or closed  When the switch is open, the circuit is incomplete – no electricity can flow  What happens when the switch is closed?
  19. 19. Bulb / Lamp  The lamp lights up when electricity flows through it  What would happen to a lamp if there was an open switch in the circuit?
  20. 20. Wires The wires which carry electricity consist of two parts: • The metal wires (conductor). • The plastic coating around the metal wires (insulator). • Prevents people from being electrocuted. wires
  21. 21. Voltmeter  The voltmeter measures the voltage of the circuit  We will discuss this in another lesson
  22. 22. Ammeter  The ammeter measures the current in the circuit  We will discuss this in another lesson
  23. 23. Resistor  A resistor can change the amount of current in a circuit  In a variable resistor, the resistance can be changed.
  24. 24. Resistance
  25. 25. Variable resistors Look at Figure 17.6 on page 207. Path of current flow Terminal A  metal bar  sliding contact  coils of wire  Terminal B
  26. 26. Variable resistors Look at Figure 17.6 on page 207. The sliding contact can be adjusted so that the current passes through only a few coils of wire or many coils of wire. If the sliding contact is near Terminal A : current passes through many coils of wire = high resistance If the sliding contact is near Terminal B: current passes through a few coils of wire = low resistance
  27. 27. Variable resistors Turn the dial here for low resistance higher resistance
  28. 28. Fuse  A fuse is a safety device  When the current is too high, the fuse breaks Example The wire inside a 3A fuse will melt when the current is greater than 3A.
  29. 29. Motor  A motor can be fitted into a circuit  What do you think happens to a motor in a complete circuit?
  30. 30. Circuit Symbols Voltmeter Ammeter Variable Resistor Switch Bulb Motor Cell Battery
  31. 31. types of circuit There are two types of electrical circuits; SERIES CIRCUITS PARALLEL CIRCUITS
  32. 32. The components are connected end-to-end, one after the other. They make a simple loop for the current to flow round. SERIES CIRCUITS If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.
  33. 33. PARALLEL CIRCUITS The current has a choice of routes (paths). The components are connected side by side. If one bulb ‘blows’ there would still be a complete circuit to the other bulb so it stays lit.
  34. 34. measuring current Electric current is measured in amps (A) using an ammeter connected in series in the circuit. A
  35. 35. measuring current A A This is how we draw an ammeter in a circuit. SERIES CIRCUIT PARALLEL CIRCUIT
  36. 36. measuring current SERIES CIRCUIT PARALLEL CIRCUIT • current is the same at all points in the circuit. 6A 6A 6A • current is shared between the components 4A4A 3A 1A
  37. 37. copy the following circuits and fill in the missing ammeter readings. ? ? 4A 4A 4A 3A? ? 1A ? 3A 1A 1A
  38. 38. measuring voltage The ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeter V
  39. 39. Different cells produce different voltages. The bigger the voltage supplied by the cell, the bigger the current (the cell gives a bigger push to the electrons). measuring voltage
  40. 40. measuring voltage Unlike an ammeter a voltmeter is connected across the components (in parallel) Scientist usually use the term Potential Difference (pd) when they talk about voltage.
  41. 41. Final GPE Initial GPE Potential Difference
  42. 42. pd
  43. 43. measuring voltage V This is how we draw a voltmeter in a circuit. SERIES CIRCUIT PARALLEL CIRCUIT V
  44. 44. V measuring voltage V V V
  45. 45. series circuit 1.5V • voltage is shared between the components 1.5V 3V
  46. 46. • voltage is the same in all parts of the circuit. 3V parallel circuit 3V 3V
  47. 47. measuring current & voltage V V 6V 4A A A a)
  48. 48. measuring current & voltage V V 6V 4A A A A b)
  49. 49. answers 3V 3V 6V 4A 4A 6V 6V 6V 4A 4A 2A 2A 4A a) b)
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