Electricity
Electricity:
Electricity is one of the basic forms of energy. Electricity is associated with electric charge, a property of certain elementary particles such as electrons and protons, two of the basic particles that make up the atoms of all ordinary matter. Electric charges can be stationary, as in static electricity, or moving, as in an electric current. Electrical activity takes place constantly everywhere in the universe. Electrical forces hold molecules together. The nervous systems of animals work by means of weak electric signals transmitted between neurons (nerve cells). Electricity is generated, transmitted, and converted into heat, light, motion, and other forms of energy through natural processes, as well as by devices built by people. Electricity is an extremely versatile form of energy. It can be generated in many ways and from many different sources. It can be sent almost instantaneously over long distances. Electricity can also be converted efficiently into other forms of energy, and it can be stored. Because of this versatility, electricity plays a part in nearly every aspect of modern technology. Electricity provides light, heat, and mechanical power. It makes telephones, computers, televisions, and countless other necessities and luxuries possible.
Electric Charge:
Electricity consists of charges carried by electrons, protons, and other particles. Electric charge comes in two forms: positive and negative. Electrons and protons both carry exactly the same amount of electric charge, but the positive charge of the proton is exactly opposite the negative charge of the electron. If an object has more protons than electrons, it is said to be positively charged. If an object has more electrons than protons, it is said to be negatively charged. If an object contains as many protons as electrons, the charges will cancel each other and the object is said to be uncharged, or electrically neutral. Electricity occurs in two forms: static electricity and electric current. Static electricity consists of electric charges that stay in one place. An electric current flows between objects or locations.
Static Electricity:
Static electricity can be produced by rubbing together two objects made of different materials. Electrons move from the surface of one object to the surface of the other if the second material holds onto its electrons more strongly than the first does. The object that gains electrons becomes negatively charged, since it now has more electrons than protons. The object that gives up electrons becomes positively charged. For example, if a nylon comb is run through clean, dry hair, some of the electrons on the hair are transferred to the comb. The comb becomes negatively charged and the hair becomes positively charged.
A. Charging by Contact:
Objects become electrically charged in either of two ways: by contact or by induction. A charged object transfers electric charge to an object with lesser charge if the two touch. When this happens, a charge flows from the first to the second object for a brief time. Charges in motion form an electric current. When charge flows between objects in contact, the amount of charge that an object receives depends on its ability to store charge. The ability to store charge is called capacitance and is measured in units called farads. The flow of charge between objects with different amounts of charge will occur whenever possible. However, it requires a pathway for the electric charge to move along. Some materials, called conductors, allow an electric current to flow through them easily. Other materials, called insulators, strongly resist the passage of an electric current. Under normal conditions, air is an insulator. However, if an object gains a large enough charge of static electricity, part of the charge may jump, or discharge, through the air to another object without touching it directly. When the charge is large enough, the air becomes a conductor. Lightning is an example of a discharge.
B. Charging by Induction:
A charged object may induce a charge in a nearby neutral object without touching it. For example, if a positively charged object is brought near a neutral object, the electrons in the neutral object are attracted to the positive object. Some of these electrons flow to the side of the neutral object that is nearest to the positive object. This side of the neutral object accumulates electrons and becomes negatively charged. Because electrons leave the far side of the neutral object while its protons remain stationary, that side becomes positively charged.
Since the negatively charged side of the neutral object is closest to the positive object, the attraction between this side and the positive object is greater than the repulsion between the positively charged side and the positive object. The net effect is an attraction between the objects. Similarly, when a negatively charged object is brought near a neutral object, the negative object induces a positive charge on the near side of the neutral object and a negative charge on the far side. These induced charges are not permanent. As soon as the charged object is taken away, the electrons on the other object redistribute themselves evenly over it, so that it again becomes neutral.
An object can also be charged permanently by induction. If a negatively charged object, A, is brought near a neutral object, B, the electrons on B are repelled as far as possible from A and flow to the other side of B. If that side of B is then connected to the ground by a good conductor, such as a metal wire, the electrons flow out through the wire into the ground. The ground can receive almost any amount of charge because Earth, being neutral, has an enormous capacitance. Object B is said to be grounded by the wire connecting it to Earth.
Coulomb's Law:
Objects with opposite charges attract each other, and objects with similar charges repel each other. Coulomb's law, formulated by French physicist Charles Augustin de Coulomb during the late 18th century, quantifies the strength of the attraction or repulsion. This law states that the force between two charged objects is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. The greater the charges on the objects, the larger the force between them, and the greater the distance between the objects, the lesser the force between them. The unit of electric charge, also named after Coulomb, is equal to the combined charges of 6.24 � 1018 protons (or electrons). If two charged objects in contact have the same capacitance, they divide the charge evenly.