Electricity
Electricity is an invisible force that can produce heat, light, motion and many other physical effects. The force is an attraction or repulsion between electrical charges. More specifically, electricity can be explained in terms of electrical charge, current, voltage, and resistance. the corresponding electrical units are the coulomb for measuring electrical charge, the ampere for measuring current, the volt for potential difference, and the ohm for resistance. A basic element of electricity is the electric circuit. A circuit is a closed path that allows for movement of charges. Current is the name given to the movement of charges. The study of electricity involves the behavior of charges, current and voltage with the components that make up the electrical circuit. Electrical engineering has allowed many practical advances to be made, such as replacing steam powered trains with more efficient electric ones.
Polarity
All materials that are known contain two basic components of electric charge: the proton and the electron. The proton is a basic particle with positive polarity, and the electron is the smallest amount of electric charge having negative polarity. It is an arrangement of electrons and protons as basic particles of electricity that determines the electrical characteristics of substances. Although all matter has protons and electrons, most materials do not exhibit any evidence of electricity, because the number of protons and electrons are equal. The opposite electrical forces cancel each other out, and render materials like paper electrically neutral. In order to use electricity to do work, the protons and electrons must be separated. A battery can do electrical work because a chemical process separates electric charges to create an excess of of electrons at its negative terminal and conversely, an excess of protons at its positive terminal. With separate and opposite charges at two terminals, electric energy can be supplied to a circuit connected to the battery.
The Structure of an Atom Determines its Electrical Characteristics
Although there are many possible ways protons and electrons could group themselves, they assemble in specific combinations that result in stable arrangement. Each stable arrangement of protons, electrons, and often neutrons makes one particular kind of atom, an element. Electrons orbit the nucleus of protons and neutrons at specific intervals, called "shells" or "energy levels." Each shell has a maximum number of electrons for stability. It is the structure of the outermost shell of electrons in an element that determines how well it conducts electricity and its magnetic properties. If an element has fewer than eight electrons in its outermost shell, it can conduct electricity to some degree; the elements that have one electron in their outermost shell conduct electricity best. Gold, silver, and copper are the best conductors of electricity because their outermost electron shell has only one electron, and this allows the freest flow of electrical current because the opposition of an atom of these elements from taking on or loosing electrons is low. Materials with electrons that tend to stay in their own orbits are called insulators, because they do not conduct electricity very well. However, these materials (except for the inert gases) can also take up extra electrons to complete their outer shells, and become negatively charged; they hold on to and store electrical charge, unlike conductors. Insulating materials like glass, plastic, rubber, paper, air, and mica are called dielectrics, meaning that they can take on and hold electrical charge. Insulators are useful when it is necessary to prevent current flow. They are also used in applications for storing electrical charge, as in capacitors, since a good conductor of electricity cannot store any charge. Materials that can conduct more electrical charge than insulators, but less than conductors are called semiconductors. Carbon, silicon, and germanium are commonly used for transistors and other semiconductor components, with silicon being the most widely used.
Resources
Grob, Bertand Basic Electronics Fifth edition, 1984
