5-6

• Capacitance


  A property of an electric non-conductor that permits the storage of energy
• Capacitance


  The ratio of the magnitude of the charge per volts
• Capacitance formula


  C = q/V
• Farad (F)


  The SI unit of capacitance
• Capacitance will always be a positive quantity
• The capacitance of a given capacitor is constant
• Capacitance


  A measure of the capacitor's ability to store charge
• The farad is a large unit, typically you will see microfarads (mF) and picofarads (pF)
• Compute the capacitance


  1. Value of charge stored

  2. Volt supply
• Determine the volt supply

  1. Capacitance value

  2. Charge stored
• Capacitors


  Devices that store electric charge
• Where capacitors are used


  • Radio receivers
  • Filters in power supplies
  • Energy-storing devices in electronic flashes
• Capacitor


  Consists of two conductors called plates
• When the conductor is charged, the plates carry charges of equal magnitude and opposite directions
• A potential difference exists between the plates due to the charge
• Dielectric


  A non-conducting material that, when placed between the plates of a capacitor, increases the capacitance
• Dielectrics


  • Rubber
  • Glass
  • Waxed paper
• Variables affecting capacitance


  • Area of conducting plate
  • Distance between the conducting plates
  • Type of Dielectrics
• Area of conducting plate

  Increase capacitance
• Distance between the conducting plates

  Increase capacitance
• More conducting dielectrics


  Decrease capacitance
• Less conducting/more insulating dielectrics

  Increase capacitance
• Leakage current


  Small amount of current that manage to pass through even with the dielectrics blocking their way
• Shapes of capacitors


  • Parallel-plate
  • Cylindrical
  • Spherical
• Parallel-plate capacitor


  • Each plate is connected to a terminal of the battery
  • The battery is a source of potential difference
  • If the capacitor is initially uncharged, the battery establishes an electric field in the connecting wires
• Cylindrical capacitor


  • The inner and outer cylinder structures correspond to the plates in the parallel-plate capacitor
  • The value of the capacitance is directly proportional to each length and cross-sectional area
• Spherical capacitor


  • Almost similar to the construction of the cylindrical capacitor
  • The value of the capacitance is directly proportional to the overall radius
  • Voltage on this type is also intensified by increasing the radius
• Capacitors in a circuit


  • Series connection
  • Parallel connection
• Series connection


  1. Total charge stored is constant

  2. Total voltage varies

  3. Total capacitance is reciprocal of sum of reciprocals
• Parallel connection


  1. Total charge is sum of individual charges

  2. Total voltage is constant

  3. Total capacitance is sum of individual capacitances
• Compute the total values

  1. Capacitance

  2. Voltage

  3. Charge
• Applications of capacitance


  • Charged parallel-plate capacitors
  • Batteries and electroscopes
  • Camera flash lamps
  • Geiger counters
  • Coaxial cables
• Charged parallel-plate capacitor


  • Dependent on the area and the distance between charged plates
  • C = K.ε0.A/d
• Compute the capacitance of a parallel-plate capacitor

  1. Area of plates

  2. Distance between plates
• Battery


  Convenient source of electric energy
• Electroscope


  Effective storage of electrical charges
• Camera flash lamps


  Use electronic flash lamps connected in an electric circuit that charges a capacitor
• Geiger counter


  Used to measure ionizing radiation, made up of a tube filled with noble gases with high voltage applied
• Coaxial cables


  Have a cylindrical capacitor structure, primarily used in local area networking
• Electrical circuits facilitate the delivery of electrical energy through current flow which moves to electrically powered equipment