Electricity

• Energy appears in many forms
• Electrical devices can change electric energy into other forms of energy, such as light and heat
• Other technology can transform heat, light and energy of movement (kinetic energy) into electrical energy
• Electricity and Heat


  In appliances, electric energy is converted to heat as moving charges meet the resistance of a metal conductor
• Thermocouple


  A loop of two wires made of different types of metals, where when one junction is heated, a small electric current is produced
• The basic principle of the thermocouple was discovered by Thomas Johann Seebeck in 1821, and was named the Seebeck Effect
• Copper and constantan (a copper nickel alloy), or iron and constantan, are the most common metals used in modern industrial thermocouples
• Individual thermocouples produce only a small amount of current, but they are widely used to obtain accurate temperature measurements where regular liquid thermometers cannot be used
• Thermo-electric generator


  A device based on a thermocouple that converts heat directly into electricity without moving parts
• Thermo-electric generators can range in output size from 15–550 W and can be combined to produce up to 5000 W
• Piezoelectric effect


  When a piezoelectric crystal such as quartz or Rochelle salt is connected to a potential difference, the crystal expands or contracts slightly, which can create sound waves or vibrations
• The link between electricity and pressure was first investigated in 1880 by two young French scientists, Pierre and Jacques Curie
• Modern researchers have developed non-crystalline materials that move in response to an electric current, with many potential uses
• Motion to Electricity


  When a piezoelectric crystal is being compressed or pulled, a potential difference builds up on opposite sides of the crystal, which can be used to create a spark or control electric currents
• Striking the quartz crystals together produces flashes of light due to the piezoelectric effect
• In 1927, Warren Morrison, a Canadian engineer working for Bell Laboratories in the United States, invented the quartz clock and revolutionized the way time was kept
• Quartz crystals


  Vibrate when a voltage from a battery is applied to them
• Quartz watch crystals act as miniature tuning forks that vibrate 32 768 times per second
• Other types of crystals vibrate at more than 50 million times per second
• Light-emitting diodes (LEDs)


  Solid-state electronic components that glow when electricity flows through them
• LEDs use only a fraction of the power of a traditional bulb and last for years as opposed to months
• Photovoltaic (PV) cell or solar cell


  Device that is most commonly used to produce electricity from light
• Photovoltaic cells are made of semiconducting materials such as silicon
• When light strikes the cell, some light is absorbed by the semiconductor material, breaking electrons loose and allowing them to flow freely
• Metal contacts on the top and bottom of the PV cell allow this electric current to be drawn off for external use
• Because voltage and current of an individual cell are limited, solar cells are usually combined to form modules, which are in turn combined to form arrays
• Many fish have electric organs that can produce a large voltage. They use this electric energy to detect enemies, navigate, and possibly to communicate.
• The South American fresh water eel, Electrophorous electricus, can generate the largest voltage of any fish. The electric organ consists of thousands of flat, specialized muscle cells, called electroplaques, which make up about 40% of the eel's mass. Each cell generates a voltage of about 0.15 V. Because the cells are connected in series, the electric organ can generate a total voltage of about 600 V.
• When things are rubbed together


  1. Allows electrons to build up on one of the items

  2. Causes unbalanced charges

  3. Usually insulators
• If charge is built up on an object


  It may stick to or be attracted to something else as it will make the charges in the other thing move to attract unlike charges and repel like charges
• If something has built up a charge


  1. Comes near or in contact with a conductor

  2. Releases the electrons

  3. Causes static discharge

  4. Shock or spark from electrons moving
• Law of Charges


  • Unlike charges attract
  • Like charges repel
  • Charged objects attract uncharged (neutral) objects
• Conductors vs insulators


  • Examples of good conductors
  • Examples of good insulators
• Semiconductors


  Examples of them
• Superconductors


  • What they do
  • How they do it (temperatures)
  • Where used/why important
• Electric discharge


  Can be a safety hazard
• Static electricity


  Static electricity is caused by the accumulation (charge at rest) of charge on the surface of the body.
• Parts of circuits


  • Sources
  • Conductors
  • Loads
  • Controls
• Series vs. Parallel circuits


  • Series: Only one path for electrons. It is a continuous loop. Electrons flow through everything in the loop.
  • Parallel: Multiple paths or branches for current to flow through
• Electrical current


  • Symbol = I
  • Measured by ammeters and galvanometers
  • Units = amperes/amps or milliamps (A, mA)