Read the text. In all history no discovery has had such an effect on human existence as electricity

Electricity

In all history no discovery has had such an effect on human existence as electricity. Our homes are lit by electric lamps of various types. Electricity plays an important part in heating our homes. Household appliances by the dozen make our daily lives easier. Our cars and lorries, though run on petrol, must have their fuel ignited by an electric spark.

The field of communication, including telephone, radio and telemetry from outer space, is only possible through the use of electricity. The development of industry depends upon electric motors of thousands of kilowatts that drive our large machines. “Electricity” is the only word that has been used so far to describe the phenomenon of energy conversion. The invisible current, however, is the medium by which the more general form “electricity” carries out its mission. An electric current flows in a material if its atoms have free charged particles (positive ions) or electrons (negatively charged particles) that can actually move from one atom to another. All metals have this characteristic. Some (such as silver, copper, or aluminum) have a large number of free electrons in their atomic structure and. therefore, are good conductors of electricity. In the presence of an electric field these free electrons will move from atom to atom through a conductor.

This part of electrical phenomenon is referred to as current flow.

Numerous scientific developments have occurred in the 19th century, many of which can be attributed to the phenomenal expansion of electrical principles and applications. In the early years of the twentieth century, electricity was just beginning to be used as a source of energy in the fields of illumination, power, and communication. During the past years, the great advances made in the many new users of electricity have affected the lives of men all over the world.

Electrical energy is used in varying quantities and is produced by several methods in order to meet a wide range of power requirements. The large power plants near our population centers and industrial areas are familiar sights. Such power plants supply millions of kilowatt-hours of electrical energy for operating lights, home appliances, industrial equipment, communication equipment, and railway transportation equipment. The large amounts of power required by these services may be produced by converting heat energy (obtained from coal, oil, gas, or atomic reactors) to electrical energy converting water power to electrical energy.

Another widely used source of electrical energy is the chemical cell which converts stored chemical energy to electrical energy. Two familiar applications of this type of power source are the primary cell, as used in transistor radio receivers and electronic test equipment, and the secondary cell, as used in storage batteries for automobiles.

A relatively new source of electrical energy is the solar cell which converts light energy, obtained from the sun, to electrical energy. This type of power source is now being used in the control and monitoring equipment for satellite and space vehicles and is providing our scientists with much new information about outer space.

Another new source of electrical energy is the fuel cell. This type of cell, unlike the ordinary chemical cell, does not store energy but, rather, converts the energy from conventional fuel oxidation directly to electrical energy. The fuels used are of the inexpensive fossil types, such as coal and hydrocarbons or substances easily derived from them, such as hydrogen, alcohol, carbon monoxide, etc.