1 / 49

Introduction to Electricity

Introduction to Electricity. John R. Ebden. Seneca College. What is electricity?. Static electricity Current Voltage Resistance AC DC. ?. Atoms and electrons. Electronics is based on controlling the movement of electrons . Static electricity .

sugar
Download Presentation

Introduction to Electricity

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Introduction to Electricity John R. Ebden Seneca College

  2. What is electricity? • Static electricity • Current • Voltage • Resistance • AC • DC ? Introduction to Electricity

  3. Atoms and electrons • Electronics is based on controlling the movement of electrons Introduction to Electricity

  4. Static electricity • Rubbing objects can cause electrons to be added or removed from the object. • The object then becomes charged because it no longer has the same number of electrons as protons. - + + + Unlike charges attract Like charges repel Introduction to Electricity

  5. Static electricity • When a plexiglass rod is rubbed with a silk cloth, electrons move from the rod to the cloth, leaving the rod positively charged, and the cloth negatively charged. Introduction to Electricity

  6. Static electricity • If the now positively charged rod is placed near your hair, it will cause the electrons in your hair to move towards the end of the hair. • Your hair will become attracted to the positive charged rod making it stand up. Introduction to Electricity

  7. Static electricity • Static electricity occurs when electric charges build up on an object, but the electric charges cannot move around. He is charged up !! He just lost his charge !! Introduction to Electricity

  8. Static electricity • Static electricity is a big problem for companies that deal with non-conducting materials like plastics. • The high voltages can destroy sensitive electronic components • At companies like Celestica personnel must wear ESD coats, work on ESD surfaced tables, and wear grounded wrist straps Introduction to Electricity

  9. Current electricity • There is another type of electricity, current electricity, which consists of a continuous flow of electrons. • It requires a source of electrons and a pathway to carry or conduct them. • The source of electrons might be a battery or a generator. G Introduction to Electricity

  10. Current electricity • Current electricity must flow along a pathway, usually metal, called a conductor. • Copper , aluminium , and gold are common conductors. • Some materials prevent the flow of electrons and are called insulators. Introduction to Electricity

  11. Current electricity • A bulb or an electric appliance may be part of that pathway. Electrons are returned to the battery or generator along the pathway completing the electric circuit. Introduction to Electricity

  12. Voltage • Current electricity flows because there is a difference in electrical pressure or potential between two points along a conductor. • This potential difference is called voltage. Introduction to Electricity

  13. Direct current (DC) and alternating current (AC) • Electric circuits can be connected to either a direct current (DC) or an alternating current (AC) electricity supply. Introduction to Electricity

  14. Direct current (DC) • The stream of electrons flow in only one direction around the circuit, from the negative terminal to the positive terminal Introduction to Electricity

  15. Direct current (DC) • In the early days, the concept of electron flow was not fully understood so scientists randomly decided that current in a conductor flowed from the positive terminal and into the negative terminal. • It is still convention today to show current flowing in this direction (ie. opposite to electron flow). Introduction to Electricity

  16. Alternating current (AC) • The electrons move backwards and forwards around an electric circuit in this case Introduction to Electricity

  17. How electricity is made • AC (most common) is made using a generator. • DC is made by: • batteries (chemical reaction) • power supplies (rectification of AC) Introduction to Electricity

  18. DC Sources - Batteries Introduction to Electricity

  19. DC Sources – Power Supplies Introduction to Electricity

  20. Making AC • AC Electricity can be made or generated by moving a wire (conductor) through a magnetic field. Introduction to Electricity

  21. Magnetism • A bar magnet has a north and south pole. It is placed under a sheet of paper and iron filings are sprinkled over the top of the paper. • These lines of filings show the magnetic field around the magnet. Introduction to Electricity

  22. Making AC • If a coil of wire is moved within a magnetic field electricity is produced in the coil. • As loop is “cutting” more lines of magnetic field when it is horizontal, the current is a maximum. Introduction to Electricity

  23. Making AC • When loop is vertical no magnetic field lines are being “cut”, and current is zero. Introduction to Electricity

  24. Making AC • When loop has rotated 180o it is flat again. • Current is now maximum but in the opposite direction. Introduction to Electricity

  25. Making AC • The current produced changes direction every half turn (180 degrees ). This is called alternating current or AC. • The generators at large power stations produce nearly all the electricity we use in this way. Introduction to Electricity

  26. Making AC • The voltage in the loop varies with angle as shown. Introduction to Electricity

  27. Making AC • 1 rev = 1 cycle = 360 degrees • domestic supply = 60 cycles/sec = 60 Hz •  loop rotates at 60 rev/sec = 3600 rpm Introduction to Electricity

  28. Making AC • In many parts of Europe the frequency employed is 50 Hertz (cycles/sec) Introduction to Electricity

  29. Making AC • 3 phase current is used to supply commercial buildings as it is more efficient. • Produced by 3 loops rather 1 Introduction to Electricity

  30. Current • Can compare water flowing through a pipe with current in a conductor “flow of electrons” Introduction to Electricity

  31. Current • A flow meter measures the water flow in litres/sec • An ammeter measures the current in A (1 A = 6.24  1018 electrons/sec) Introduction to Electricity

  32. Current 1 Coulomb (C) = charge carried by 6.24  1018 electrons 1 Ampere = 1Coulomb/second (A = C.sec-1) Introduction to Electricity

  33. Current • The movement of charge is called electric current. • The more electrons per second that pass through a circuit, the greater the current. • Current is the rate of flow of charge. I = Q/t Introduction to Electricity

  34. Voltage • A pump can be used to cause the water to flow in the pipe. • The force that makes the water flow is called pressure (measured in Pa or psi) Introduction to Electricity

  35. Voltage • A generator is an electrical “pump” • The electrical pressure is called electrical potential or voltage (measured in V) Introduction to Electricity

  36. Voltage Force between charges is: F = kQ1Q2/r2 To separate unlike charges (or bring like charges together) work is done W = Force x distance W = Fdx Introduction to Electricity

  37. Voltage • When two objects have a difference in charges, we say they have a potential difference or voltage between them. • The unit of voltage is the volt. • Thunderclouds have hundreds of millions of volts between them. Introduction to Electricity

  38. Voltage Introduction to Electricity

  39. Voltage • A difference in potential energy is defined as voltage. • The voltage between two points is one volt if it requires one joule of energy to move one coulomb of charge from one point to another. • V = Work/Charge or V = W/Q • Volt = Joule/Coulomb • Voltage is defined between points. Introduction to Electricity

  40. Ammeters and voltmeters • Ammeters are connected into the circuit. The circuit must be “broken” to put one in. • Voltmeters are connected across components to measure voltage. No need to break the circuit Note: voltage does not flow, current does Introduction to Electricity

  41. Measuring voltage • Voltmeter is placed in parallel • No need to change circuit Introduction to Electricity

  42. Measuring current • Ammeter is placed in series • Will need to “break” the circuit Introduction to Electricity

  43. Resistance • When water flows in a pipe, its flow is impeded by factors such as the size of the pipe, roughness of the pipe, etc. • Anything that impedes or resists current flow in a circuit is called resistance. Introduction to Electricity

  44. Resistance • Electrical resistance is measured with an ohmmeter. Units are ohms () • The power must be off before making any measurements. Introduction to Electricity

  45. Ohm’s Law • Relates current, voltage and resistance: I = V/R or, V = IR or, R = V/I Introduction to Electricity

  46. Example - What is the current? Lamp has resistance of 96  and battery is 12 V I = 12V/96 = 0.125A = 125x10-3A = 125mA Introduction to Electricity

  47. Meters - Analogue (VOM) Introduction to Electricity

  48. Meters - Digital (DMM) Introduction to Electricity

  49. Meters - Oscilloscope • Used for analysing waveforms Introduction to Electricity

More Related