What is Electricity?

Author: S.Ashok

Electrons travel around the nucleus of an atom and are held in their orbits by the attraction of the positive charge in the nucleus. if somehow force an electron out of its orbit, then the electron’s action would become what is known as electricity.

Six sources of electricity

To produce electricity, some form of energy must be used to bring about the action of electrons. The six basic sources of energy which can be used are FRICTION, PRESSURE, HEAT, LIGHT, MAGNETISM and CHEMICAL ACTION.

What is static electricity?

Electrons which are forced out of their orbits in some way will leave a lack of electrons in the material which they leave and will cause an excess of electrons to exist at the point where they come to rest. This excess of electrons in one material is called a “negative” charge while the lack of electrons in the other material is called a “positive” charge. When these charges exist you have what is called “static” electricity.

How friction produces electricity?

When two materials rub together, due to friction contact, some electron orbits of the materials cross each other and one material may give up electrons to the other. If this happens, static charges are built up in the two materials, and friction has thus been a source of electricity. The charge which you might cause to exist could be either positive or negative depending on which material gives up electrons more freely.

When glass is rubbed with silk, the glass rod loses electrons-the rod becomes positively charged and the silk negatively charged.

If materials with strong charges, the electrons may jump from the negative charge to the positive charge before the two materials are actually in contact. In that case, you would actually see the discharge in the form of an arc. With very strong charges, static electricity can discharge across large gaps, causing arcs many feet in length.

Lightning is an example of the discharge of static electricity resulting from the accumulation of a static charge in a cloud as it moves through the air. Natural static charges are built up wherever friction occurs between the air molecules, such as with moving clouds or high winds, and you will find that these charges are greatest in a very dry climate, or elsewhere when the humidity is low.

How pressure produces electricity

Whenever you speak into a telephone, or other type of microphone, the pressure waves of the sound energy move a diaphragm. In some cases, the diaphragm moves a coil of wire past a magnet, generating electrical energy which is transmitted through wires to a receiver. Microphones used with public address systems and radio transmitters sometimes operate on this principle. Other microphones, however, convert the pressure waves of sound directly into electricity.

Crystals of certain materials will develop electrical charges if a pressure is exerted on them. Quartz, tourmaline, and Rochelle salts are materials which illustrate the principle of pressure as a source of electricity. If a crystal made of these materials is placed between two metal plates and a pressure is exerted on the plates, an electric charge will be developed. The size of the charge produced between the plates will depend on the amount of pressure exerted.

the crystal can be used to convert electrical energy to mechanical energy by placing a charge on the plates, since the crystal will expand or contract depending on the amount and type of the charge.

How heat produces electricity

Another method of obtaining electricity is to convert heat into electricity directly, by heating a junction of two dissimilar metals. For example, if an iron wire and a copper wire are twisted together to form a junction, and the junction is heated, an electric charge will result. The amount of charge produced depends on the difference in temperature between the junction and the opposite ends of the two wires. A greater temperature difference results in a greater charge.

A junction of this type is called a thermo-couple and will produce electricity as long as heat is applied. While twisted wires may form a thermo- couple, more efficient thermo-couples are constructed of two pieces of dissimilar metal riveted or welded together.

How light produces electricity

Electricity may be produced by using light as the source of energy con- verted to electricity. When light strikes certain materials, they may con- duct electric charges easier, develop an electric charge, emit free electrons or convert light to heat.

The most useful of these effects is the development of an electric charge by a photo cell when light strikes the photo -sensitive material in the cell.

A photo cell is a metallic “sandwich” or disc composed of three layers of material. One outside layer is made of iron. The other outside layer is a film of translucent or semi transparent material which permits light to pass through. The centre layer of material is composed of selenium alloy. The two outside layers act like electrodes. When light is focused on the selenium alloy through the translucent material an electric charge is developed between the two outside layers. If a meter is attached across these layers the amount of charge can be measured. A direct use of this type of cell is the common light meter as used in photography for determining the amount of light which is present.

How chemical action produces electricity

Batteries are usually used for emergency and portable electric power. Whenever you use a flashlight emergency light or portable equipment, you will be using batteries. Batteries are the main source of power for present day submarines. In addition, there is a wide variety of equipment which uses cells or batteries either as normal or emergency power. “Dead” batteries are a common type of equipment failure and such failures can be very serious.

Cells and batteries require more care and maintenance than most of the equipment on which you will work. Even though you may use only a few cells or batteries, if you find out how they work, where they are used and how to properly care for them, you will save time and in many cases a lot of hard work.

To find out how the chemical action in batteries works, you might imagine that you can see electrons and what happens to them in a primary electric cell. The basic source of electricity produced by chemical action is the electric cell and, when two or more cells are combined, they form a battery.

First you would notice the parts of the cell and their relation to each other. You would see a case or container in which two plates of different metals, separated from each other, are immersed in the liquid which fills the container.

Watching the parts of the cell and the electrons in the cell you would see that the liquid which is called the electrolyte is pushing electrons onto one of the plates and taking them off the other plate. This action results in an excess of electrons or a negative charge on one of the plates so that a wire attached to that plate is called the negative terminal. The other plate loses electrons and becomes positively charged so that a wire attached to it is called the positive terminal.

The action of the electrolyte in carrying electrons from one plate to the other is actually a chemical reaction between the electrolyte and the two plates. This action changes chemical energy into electrical charges on the cell plates and terminals.

How magnetism produces electricity

The most common method of producing electricity used for electric power is by the use of magnetism. The source of electricity must be able to maintain a large charge because the charge is being used to furnish electric power. While friction, pressure, heat and light are sources of electricity, you have found that their use is limited to special applications since they are not capable of maintaining a large enough charge for electric power.

All of the electric power used, except for emergency and portable equipment, originally comes from a generator in a power plant. The generator may be driven by water power, a steam turbine or an internal combustion engine. No matter how the generator is driven, the electric power it pro- duces is the result of the action between the wires and the magnets inside the generator.

When wires move past a magnet or a magnet moves past wires, electricity is produced in the wires because of the magnetism in the magnetic material. Now you will find out what magnetism is and how it can be used to produce electricity.

Magnetism is an invisible force and can be seen only in terms of the effect it produces. You know that the wind, for example, provides tremendous force, yet it is invisible. Similarly, magnetic force may be felt but not seen.

The magnetic field about a magnet can best be explained as invisible lines of force leaving the magnet at one point and entering it at another. These invisible lines of force are referred to as “flux lines” and the shape of the area they occupy is called the “flux pattern.” The number of flux lines per square inch is called the “flux density.” The points at which the flux lines leave or enter the magnet are called the “poles.” The magnetic circuit is the path taken by the magnetic lines of force.

Electricity produced by relative movement of a magnet and a wire that results in the cutting of lines of force.