Electricity is the movement of electric charge, commonly known as electric current. The ease with which this charge flows through a material is called electrical conductivity. Materials are categorized by their ability to conduct electricity: some allow flow easily, others resist it significantly, and a unique group offers controllable conductivity.
Understanding Electrical Flow
Electricity flows through materials primarily via two mechanisms. In solid metals, current is carried by free electrons. These electrons are not tightly bound to individual atoms; instead, they form a “sea” that moves throughout the material when an electrical force is applied, constituting the electric current.
In liquid solutions or molten substances, electricity is conducted by the movement of ions. Ions are atoms or molecules with a net positive or negative charge due to gaining or losing electrons. When dissolved, these charged particles become mobile and move towards oppositely charged electrodes, carrying the current. This process differs from electron flow as it involves the physical migration of atoms or molecules.
Materials That Readily Conduct
Electrical conductors are materials that allow electric current to pass through them. Metals are excellent conductors because their atomic structure features loosely bound outer electrons that move freely throughout the material. This “sea” of mobile electrons enables metals like copper, silver, gold, and aluminum to efficiently transfer charge. Aluminum is also valued for its light weight and good conductivity.
Certain liquids also conduct electricity through electrolytic conduction. This occurs when substances like salts, acids, or bases dissolve in a solvent, dissociating into mobile positive and negative ions. Saltwater, for instance, conducts electricity because sodium chloride breaks down into charged sodium and chloride ions that carry current. Plasma, an ionized gas, also exhibits high electrical conductivity due to free electrons and ions.
Materials That Resist or Block Flow
Materials that impede the flow of electricity are classified as electrical insulators. In these substances, electrons are tightly bound to their respective atoms and are not free to move throughout the material. This strong atomic binding means there are very few mobile charge carriers available to conduct an electric current. Common examples of insulators include rubber, plastic, glass, and wood.
Pure water also acts as a poor conductor because it contains very few free ions. Insulators are used to protect against electric shock and to direct the flow of electricity along desired paths in electrical systems. While no material is a perfect insulator, these substances offer very high electrical resistance, effectively blocking the passage of current under normal conditions.
The Unique Nature of Semiconductors
Semiconductors represent a distinct category of materials with electrical conductivity falling between good conductors and effective insulators. Their unique property lies in their ability to control or modify their conductivity. Unlike conductors, semiconductors do not have an abundance of free electrons at room temperature, but unlike insulators, their electrons are not so tightly bound that they cannot be made to move.
The conductivity of semiconductors can be precisely adjusted through processes like doping, where small amounts of impurities are intentionally added to the material. Changes in temperature can also influence their conductivity; for instance, as temperature increases, the conductivity of semiconductors generally increases. Silicon and germanium are prominent examples of semiconductors, forming the basis of many modern electronic components such as computer chips, transistors, and solar cells. Their controllable conductivity makes them indispensable for the precise control of electrical signals in technology.