electricity

Electricity

Electricity is the set of physical phenomena associated with the presence and flow.
11. Electromagnetic wave
Faradays and Amp
12. Generation and transmission
In the 6th century BC, the Greek philosopher Thales of Miletus experimented with amber rods and these experiments were the first studies into the production of electrical energy. While this method, now known as the triboelectric effect, can lift light objects and generate sparks, it is extremely inefficient. It was not until the invention of the voltaic pile in the eighteenth century that a viable source of electricity became available. The voltaic pile, and its modern descendant, the electrical battery, store energy chemically and make it available on demand in the form of electrical energy. The battery is a versatile and very common power source which is ideally suited to many applications, but its energy storage is finite, and once discharged it must be disposed of or recharged. For large electrical demands electrical energy must be generated and transmitted continuously over conductive transmission lines.

Electrical power is usually generated by electro mechanical generators driven by steam produced from fossil fuel combustion, or the heat released from nuclear reactions; or from other sources such as kinetic energy extracted from wind or flowing water. The modern steam turbine invented by Sir Charles Parsons in 1884 today generates about 80 percent of the electric power in the world using a variety of heat sources. Such generators bear no resemblance to Faradays homopolar disc generator of 1831, but they still rely on his electromagnetic principle that a conductor linking a changing magnetic field induces a potential difference across its ends. The invention in the late nineteenth century of the transformer meant that electrical power could be transmitted more efficiently at a higher voltage but lower current. Efficient electrical transmission meant in turn that electricity could be generated at centralised power stations, where it benefited from economies of scale, and then be despatched relatively long distances to where it was needed.

13. Physiological effects
A voltage applied to a human body causes an electric current through the tissues, and although the relationship is non linear, the greater the voltage, the greater the current.The threshold for perception varies with the supply frequency and with the path of the current, but is about 0.1 mA to 1 mA for mains frequency electricity, though a current as low as a microamp can be detected as an electrovibration effect under certain conditions.If the current is sufficiently high, it will cause muscle contraction, fibrillation of the heart, and tissue burns.The lack of any visible sign that a conductor is electrified makes electricity a particular hazard. The pain caused by an electric shock can be intense, leading electricity at times to be employed as a method of torture. Death caused by an electric shock is referred to as electrocution. Electrocution is still the means of judicial execution in some jurisdictions, though its use has become rarer in recent times.
14. Electricity in physics
Electricity works because electric charges push and pull on each other. There are two types of electric charges positive charges and negative charges. Similar charges repel each other. This means that if you put two positive charges close together and let them go, they would move apart. Two negative charges also repel. But different charges attract each other. This means that if you put a positive charge and a negative charge close together, they would smack together. A short way to remember this is the phrase opposites attract, likes repel.

Electric charges push or pull on each other if they are not touching. This is possible because each charge makes an electric field around itself. An electric field is an area that surrounds a charge. At each point near a charge, the electric field points in a certain direction. If a positive charge is put at that point, it will be pushed in that direction. If a negative charge is put at that point, it will be pushed in the exact opposite direction.

All the matter in the world is made of tiny positive and negative charges. The positive charges are called protons, and the negative charges are called electrons. Protons are much bigger and heavier than electrons, but they both have the same amount of electric charge, except that protons are positive and electrons are negative. Because opposites attract, protons and electrons stick together. A few protons and electrons can form bigger particles called atoms and molecules. Atoms and molecules are still very tiny. It is impossible to see them without a very powerful microscope. Any big object, like your body, has more atoms and molecules in it than anyone could count.

Because negative electrons and positive protons stick together to make big objects, all big objects that we can see and feel are electrically neutral. Electrically is a word meaning describing electricity, and neutral is a word meaning balanced. That is why we do not feel objects pushing and pulling on us from a distance, like they would if everything was electrically charged. All big objects are electrically neutral because there is exactly the same amount of positive and negative charge in the world. We could say that the world is exactly balanced, or neutral. This seems very surprising and lucky. Scientists still do not know why this is so, even though they have been studying electricity for a long time.

15. Electric voltage
Electric voltage is the push behind the current. It is the amount of work per electric charge that an electric source can do. When 1 coulomb of electricity has 1 joule of energy, it will have 1 volt of electric potential.
16. Electrical resistance
Electrical resistance is the ability of a substance to resist the flowing of the current, i.e. to reduce the amount of current that flows through the substance. If an electric voltage of 1 volt maintains a current of 1 ampere through a wire, the resistance of the wire is 1 ohm. When the flow of current is opposed resisted energy gets used or gets converted to other forms e.g. heat, etc..
17. Electric energy
Electric energy is the ability to do work by means of electric devices. Electric energy is a conserved property, meaning that it behaves like a substance and can be moved from place to place. Electric energy is measured in joules or kilowatt hours kW h.
18. Generating electricity
Electricity is mostly generated in places called power stations. Most power stations use heat to boil water into steam which turns a steam engine. The steam engines turbine turns a machine called a generator. Generators have wires inside which spin inside a magnetic field. Electromagnetic induction causes electricity to flow through the wires.

There are many sources of heat which can be used to generate electricity. Heat sources can be classified into two types renewable energy resources in which the supply of heat energy never runs out and non renewable energy resources in which the supply will be eventually used up. Sometimes a natural flow, such as wind power or water power, can be used directly to turn a generator so no heat is needed.

19. Making Electricity
In Michael Faradays generator, coils of copper wire rotating between the poles of a magnet produce a steady current of electricity. One way to rotate the disk is to crank it by hand, but this isnt a practical way to make electricity. Another option is to attach the shaft of the generator to a turbine and then let some other energy source power the turbine. Falling water is one such energy source, and, in fact, the first major plant ever built took advantage of the enormous kinetic energy delivered by Niagara Falls. George Westinghouse opened that plant in 1895, but the principles of its operation havent changed much since then. First, engineers build a dam across a river to create a reservoir of stored water. They place a water intake near the bottom of the dam wall, which allows water to flow from the reservoir and through a narrow channel called a penstock. The turbine imagine a huge propeller sits at the end of the penstock. The shaft from the turbine goes up into the generator. When the water moves across the turbine, it spins, rotating the shaft and, in turn, rotating the copper coils of the generator. As the copper coils spin within the magnets, electricity is produced. Power lines connected to the generator carry electricity from the power plant to homes and businesses. Westinghouses Niagara Falls plant was able to transport electricity more than 200 miles 322 kilometers. Not all power plants rely on falling water. Many take advantage of steam, which acts like a fluid and can therefore transfer energy to a turbine and, ultimately, to a generator. The most popular way to make steam is to heat water by burning coal. Its also possible to use controlled nuclear reactions to turn water into steam. You can read about the various types of power stations in How Hydropower Plants Work, How Wind Power Works and How Nuclear Power Works. Just keep in mind that they all work on the same basic principle of converting mechanical energy spinning turbine into electrical energy. Of course, using a generator to make electricity is just the beginning. After you get your electrons moving along, youll need an electrical circuit to do anything with it. Find out why next.
20. Electrical Circuits
When you load a battery into an electronic device, youre not simply unleashing the electricity and sending it to do a task. Negatively charged electrons wish to travel to the positive portion of the battery and if they have to rev up your personal electric shaver along the way to get there, theyll do it. On a very simple level, its much like water flowing down a stream and being forced to turn a water wheel to get from point A to point B.

Whether you are using a battery, a fuel cell or a solar cell to produce electricity, three things are always the same The source of electricity must have two terminals a positive terminal and a negative terminal. The source of electricity whether it is a generator, battery or something else will want to push electrons out of its negative terminal at a certain voltage. For example, one AA battery typically wants to push electrons out at 1.5 volts.

The electrons will need to flow from the negative terminal to the positive terminal through a copper wire or some other conductor. When there is a path that goes from the negative to the positive terminal, you have a circuit, and electrons can flow through the wire.

You can attach any type of load, such as a light bulb or motor, in the middle of the circuit. The source of electricity will power the load, and the load will perform whatever task its designed to carry out, from spinning a shaft to generating light.

Electrical circuits can get quite complex, but basically you always have the source of electricity such as a battery, a load and two wires to carry electricity between the two. Electrons move from the source, through the load and back to the source.

Moving electrons have energy. As the electrons move from one point to another, they can do work. In an incandescent light bulb, for example, the energy of the electrons is used to create heat, and the heat in turn creates light. In an electric motor, the energy in the electrons creates a magnetic field, and this field can interact with other magnets through magnetic attraction and repulsion to create motion. Because motors are so important to everyday activities and because they are, in essence, a generator working in reverse, well examine them more closely in the next section.