My Science School

Electricity is supplied to our homes, schools, factories and stores through copper or aluminium wires from power stations. These power stations burn coal or oil, use nuclear reactions or the energy of falling water to produce energy to run the generators. The power thus generated is then transmitted to different cities and places where it is required. Electricity is then transmitted through transmission lines.

To avoid the loss of power, the output voltage from the generator is first stepped up to a high voltage by a step-up transformer. After being received at the city power station, it is again reduced to low voltage, before it reaches our homes or factories. Now question arises how is electricity conducted through wires?

We know that all substances are made up of atoms. Materials which allow the passage of electricity are called conductors. Metals, such as copper, aluminium, silver and gold are good conductors of electricity. The atoms of these metals have loosely bonded electrons. These electrons are free to move within the metal. These are called free electrons and are responsible for the conduction of current. More the number of free electrons in the metal, better it conducts the electricity. 

When electric battery is connected across the ends of the metal wire, the negatively charged free electrons move away from the end connected to the negative terminals and flow toward the positive terminal. This flow of electrons is nothing but the electric current. Hence the drifting electrons cause electricity to flow. Greater the number of free electrons in a metal, easier it is for electricity to flow through it.

Some materials are poor conductors of electricity because they have less number of free electrons. Poor conductors resist the flow of electricity. The resistance of a wire depends upon its material length and area of its cross-section.

Some substances do not allow electricity to flow through them and are called insulators. These substances contain tightly-bonded electrons that cannot move away from atoms. Hence they do not conduct electricity. Glass, mica, wood, plastic and rubber are common insulators. Some substances like silicon and germanium are neither good conductors nor insulators. They are called semi-conductors. 

               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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