Category Electricity

            A good conductor such as copper has only very low electrical resistance. It does not get very hot when electricity flows through it, making copper suitable for household wiring.

            Other metals such as iron and nickel have much greater resistance to the passage of electricity, so they become hot. A very thin wire has more resistance than a thick one, and a long wire has more resistance than a short wire. In an electric fire, coils of thin, high-resistance wire glow and produce heat when an electrical current passes though them.

            In a light bulb, coils of an extremely thin conductor ensure that heat cannot be radiated away quickly enough and some of the energy is converted to light.

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               Batteries produce electricity by means of chemical action. A battery contains two different conductors, or electrodes. Usually, one of these is the metal case of the battery. The electrodes are separated by a conducting liquid or paste, called the electrolyte. The substances in the battery react chemically with each other to produce an electrical current. As a result of chemical activity a positive charge builds up at one electrode, and this can flow through a conductor such as a wire to the other (negative) electrode. Eventually the chemical energy runs out and the battery becomes exhausted.

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               Energy cannot be created. An electrical generator is simply a means of converting mechanical energy into electrical energy. In its simplest form, a generator spins coils of wire in a magnetic field, causing the flow of electrical current in the conducting wire. The power to spin the generator comes from other forms of energy. This energy might be stored energy in fossil fuels such as coal or oil, hydroelectric power from dams, wind power from turning huge windmills, or nuclear power produced by the radioactive decay of elements. In all these cases, one form of energy is simply converted into electrical energy.

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               Some materials do not have the loosely attached electrons that are needed to conduct electricity — these substances are called insulators. Rubber, most plastics, ceramics and glass are examples of good insulators. They do not allow the passage of electrical current, and so they are used to cover electrical wiring or to prevent electrical current leaking away. The more free electrons that are present in a conductor, the better it will be at conducting electrical current. Metals and many liquids are very good conductors of electricity, and some gases conduct electricity when they are very hot.

               Electricity powers our lights, heating, electronic appliances such as computers and television, and a host of other essential services that we take for granted. However, electricity has much more important aspects because it is a fundamental feature of all matter. Electricity is the force that holds together the molecules and atoms of all substances.

               The type of electricity that is most familiar to us is electrical current. This is the flow of electrical charges through a substance called a conductor, such as a metal wire. This flow happens because some of the negatively charged electrons circling the nuclei of the conductor’s atoms are held loosely. The electrons can move from one atom to the next, producing an electrical current.

               In ancient times, man had no idea of electrical energy. They took the flash of lightning during a thunder storm to be a signal for an impending destruction from the heavenly Gods. With the passage of time, science in its own way explained the mystery of this great energy called electricity.

               Today, we cannot imagine the normal life without electricity. Commonly we know it as a form of energy, that powers almost all machines or mechanical devices — trains, radios, television sets, freezers and so on. Electricity is a phenomenon involving electrical charges and their effects, when at rest as well as when in motion.

               Electricity that we use flows through wires as electric current. In a nutshell, when an electric current flows through a conductor of finite resistance, the heat energy is continuously generated at the expense of electrical energy. The particles of a matter may be positive, negative or neutral. We know that electricity has its two important particles — protons and electrons. Electron is negatively charged while proton is charged positively to an equal extent. The object containing an equal number of protons and electrons is electrically neutral. For example, anode is a positive electrode while cathode is a negative one. Bulk of the electricity we use is produced in power stations. In the generator of a power station, coils of wire are made to rotate between powerful magnets in order to rotate electric current through the coils. Electricity travels through substances like copper, aluminium and iron. These are called conductors. However, electricity cannot pass through some materials like rubber and glass and these are called insulators. 

               Electricity which flows in one direction and then in the opposite is called Alternate Current (A.C.). Each movement of A.C., back and forth, happens very quickly – about 50 times a second. The electricity that flows in our houses is mostly A.C. Steady flowing current in one direction only is known as Direct Current (D.C.). For instance, battery current is D.C.

               Soon after the invention of electric cell by Alessandro Volta, people came to know that heat, light, chemical reactions and magnetic effects could be produced from electricity.

               As early as 600 B.C. Greeks discovered electricity by rubbing Amber with cloth which enabled it to attract small pieces of papers. In fact, the word electric originated from the Greek word Electron. Based on the theory of “Electro-Magnetic Induction” of Michael Faraday in 1831, first successful generator or Dynamo was made in Germany in 1867. USA produced; electricity by running turbines with the help of falling water in 1858.

               Subsequently hydel and thermal power stations came into existence all over the world. During the 20th century many nuclear power stations were established to meet the growing demand of electricity. 

               We all know that electricity travels from one place to another through metallic wires. Can light travel through wires too?

                Light can also travel through wires, but these wires are not made of metals. They are made of glass or plastics. Light carrying wires are extremely thin and are called optical fibres. The branch of science dealing with the conduction and study of light through fibres is called Fibre Optics.

       In 1870, a British physicist John Tyndal showed that light can travel along a curved rod of glass or transparent plastic. Light travels through transparent rods by the process of total internal reflection. The sides of the fibre reflect the light and keep it inside as the fibre bends and turns. 

 

 

               The narrow fibres have a thin core of glass of high refractive index surrounded by a thin cladding of another glass of lower refractive index. The core carries light and the covering helps bend the light back to the core.

               Fibres are drawn from thick glass rods in a special furnace. The glass rod of higher refractive index is inserted in a tubing of glass of lower refractive index. Then the two are lowered carefully and slowly through a vertical furnace and the fibre drawn from the lower end is wound on a revolving drum. With this method, fibres of about .025 mm in diameter can be drawn.

               Fibres so prepared have to be aligned properly in the form of a bundle. They should not cross each other; otherwise the image transported by it will be scrambled. They are kept in straight lines. Once the aligned bundle is made, it can be bent or turned in any desired direction. 

 

 

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