Insulators and Conductors

• The number of electrons flowing past a point at a given time depends on two things: How hard the electrons are being pushed (EMF) and how much resistance is being offered by the material the electrons are going through. A good "conductor" offers very little resistance. Metals are generally good conductors. A good "insulator" strongly resists the flow of electrons. Glass and some plastics make good insulators. Electrical wires are good conductors surrounded by good insulators --- perfect avenues for the flow of electrons. One amp means that 6,241,000,000,000,000,000 electrons flow past a point in one second.
  
  

Sources of EMF

• Batteries force electron flow through chemical means. An acid removes electrons from one metal post and injects them into another post. As one post has a surplus of electrons and the other has a deficit, electrons will flow through a wire --- or circuit --- connected between the posts. Solar cells cause electrons to flow by using the energy in sunlight. Electric generators push electrons with a magnetic field. The relationship between electricity and magnetism is fundamental to the operation of many electronic devices. When electricity flows through a wire it creates a magnetic field around the wire. When a wire is moved through a magnetic field, it causes electrons to flow in the wire.
  
  

Patterns of EMF

• There are two basic types of electricity: direct current (DC) and alternating current (AC). In DC, the electrons always move in the same direction. In AC, the electrons periodically change direction. The patterns of current (electron flow) are caused by the different ways that EMF pushes the electrons. If the pressure is always in the same direction the electrons always flow in that direction --- DC. If the pressure periodically changes direction the electrons will flow first in one direction and then in the other direction direction --- AC. Batteries and solar cells produce DC, and generators produce AC. The device that changes AC to DC is called a rectifier. The device that changes DC to AC is called an alternator.
  
  

EMF Levels

• Many consumer electronic devices use DC at a level below 100 volts. When generators produce electricity, they produce AC at a level of thousands of volts. AC travels better than DC making it the preferred means for the public supply which goes to thousands of customers. At each house or business a device called a transformer "steps down" the thousands of volts to 120 volts (and sometimes 240 volts) for individual consumption. At the outlet, many devices have an additional transformer to step the voltage down to what is required. Some devices --- dishwashers, refrigerators and blenders --- use AC, but others --- radios, computers and televisions --- convert the AC to DC before using it.