Static Electricity

Static electricity refers to an imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of an electric current or electrical discharge.

Electricity by Friction

Friction produces the electric effects. The well-known example is, a hard rubber comb attract small pieces of paper after using it on a dry hair. It is because after rubbing, the comb becomes charged with electricity. The same effect is noticed when a plastic pen is rubbed on a coat sleeve. Static electricity is the electricity produced by friction between two dissimilar objects. Based on the nature of the objects, one object becomes a positive charge and the other an equal negative charge. For example, when a glass rod is rubbed with silk, the rod becomes positive charge and the silk an equal negative charge. Like charges repel and unlike charges attract.

Electrification by friction involves transfer of electrons (negatively charged particles of an atom). In the example of a glass rod rubbed with silk, some electrons from the rod transferred the silk. By losing electrons, the glass becomes positively charged and by gaining the same number of electrons silk acquires an equal negative charge.

In case of hollow metallic conductors, when they are charged with static electricity it is found that the charge remains on the outside of the conductor; the inner surface remains uncharged. This is the reason for when a car is struck by lightning, persons sitting inside are shielded from the electricity as the charge remains on the outer surface. In case of a pear-shaped conductor, the charge is concentrated on and near the pointed end. When the charge on the conductor is increased, the pointed end starts losing charge. A pointed end also acts as a collector of charge. The lightning conductor works on this principle.

Lightning Conductor

Lightning involves heavy discharge of electricity between two charged clouds or between a charged cloud and the earth. Lightning conductors are used in tall buildings for protection from lightning. A lightning conductor is a thick copper strip fixed to an outside wall of the building. The upper end of the strip consists of several sharp spikes reaching above the highest part of the building and the lower end is connected to a copper plate buried in the earth. When lightning occurs, the lightning conductor accepts any electric discharge.

Insulators, Conductors, Superconductors and Semiconductors

All the substances can be arranged based on their ability to conduct electrical charge. Almost all metals are good conductors and most non-metals are poor conductors or insulators. Metals conduct electricity as they have a large number of free electrons whereas insulators have no free electrons. With decreasing of temperature, the resistance of metals to flow of electricity reduces. At near absolute zero temperatures, metals have almost zero resistance and become superconductors. It is also discovered that certain ceramics can behave as superconductors at relatively high temperatures of above 100K. Currently, scientists are working on in the field of high temperature superconductivity hoping to achieve it at room temperatures. Materials such as silicon and germanium have electrical resistivity in between those of conductors and insulators. Such materials are called as semiconductors. They are good insulators in their pure crystalline form but their conductivity increases by adding small amounts of impurities. After the addition of impurities, they become n-type and p-type semiconductors.

Transistors

Transistors used in radios, televisions, computers and other devices are composed of both n-type and p-type semiconductors. They need very little power and in normal use they work indefinitely.

Integrated Circuits (IC)

An integrated circuit is an arrangement of multifunction semiconductor devices. It consists of a single-crystal chip of silicon containing both active and passive elements and their interconnections.