Current Affairs 8th Class

        Electricity   Electricity, one of the basic forms of energy. Electricity is associated with electric charge, a property of certain elementary particles such as electrons and protons. Electric charges can be stationary, as in static electricity, or moving, as in an electric current.   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 it 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.                   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; 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 x 1018 protons (or electrons).                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 more...

      Flame   Flame can be defined as the glowing body of mixed gases undergoing the process of combustion. Flames generally consist of a mixture of oxygen (or, air) and another gas, usually such combustible substances as hydrogen, carbon monoxide, or hydrocarbon. A typical flame is that of a burning candle. When the candle is lighted, the heat of the match melts the wax, which is carried up the wick and then vaporized by the heat. The vaporized wax is then broken down by the heat and, finally, combines with the oxygen of the surrounding air, producing a flame and generating heat and light. The candle flame consists of three zones that are easily distinguished. The innermost zone, a nonluminous zone, is composed of a gas-air mixture at a comparatively low temperature. In the second, or luminous, zone, hydrogen and carbon monoxide are produced by decomposition and begin to react with oxygen to form water and carbon dioxide, respectively. In this zone the temperature of the flame—about 590° to 680° C (about 1090° to 1250° F)—is great enough to dissociate the gases in the flame and produce free particles of carbon, which are heated to incandescence and then consumed. The incandescent carbon produces the characteristic yellow light of this portion of the flame. Outside the luminous zone is a third, invisible zone in which the remaining carbon monoxide and hydrogen are finally consumed.   All combustible substances require a definite proportion of oxygen for complete burning. In the burning of a candle, or of solids such as wood or coal, this oxygen is supplied by the surrounding atmosphere. In blowpipes and various types of gas burners, air or pure oxygen is mixed with the gas at the base of the burner so that the carbon is consumed almost instantaneously at the mouth of the burner. For this reason such flames are nonluminous. They also occupy a smaller volume and are proportionately hotter than a simple candle flame.                 Which one of the following is a solid fuel? (a) Patrol (b) CNG (c) Coal (d) LPG (e) None of these   Answer: (c)               The outermost zone of a flame is: (a) Yellow (b) Black (c) Green (d) Blue (e) None of these   Answer: (d)    

• Combustion is a process of rapid oxidation with simultaneous evolution of heat and usually light.
• Fuel is a substance that reacts chemically with another to produce energy.
• The sensation of warmth or coldness of a substance on contact is determined by the property known as temperature.
• A flame consists of three zone.
• All combustible substances require a definite proportion of more...

       Heat   Heat is the transfer of energy from one part of a substance to another, or from one body to another by virtue of a difference in temperature. Heat is energy in transit; it always flows from a substance at a higher temperature to the substance at a lower temperature, raising the temperature of the latter and lowering that of the former substance, provided the volume of the bodies remains constant.                 Temperature The sensation of warmth or coldness of a substance on contact is determined by the property known as temperature. Although it is easy to compare the relative temperatures of two substances by the sense of touch, it is impossible to evaluate the absolute magnitude of the temperatures by subjective reactions. Adding heat to a substance, however, not only raises its temperature, causing it to impart a more acute sensation of warmth, but also produces alterations in several physical properties, which may be measured with precision. As the temperature varies, a substance expands or contracts, its electrical resistivity changes, and in the gaseous form, it exerts varying pressure. The variation in a standard property usually serves as a basis for an accurate numerical temperature scale..

        Combustion   Combustion, process of rapid oxidation or burning of a substance with simultaneous evolution of heat and, usually, light. In the case of common fuels, the process is one of chemical combination with atmospheric oxygen to produce as the principal products carbon dioxide, carbon monoxide, and water, together with products such as sulphur dioxide that may be generated by the minor constituents of the fuel. The term combustion, however, also embraces oxidation in the broad chemical sense, and the oxidizing agent may be nitric acid, certain perchlorates, or even chlorine or fluorine.                  Energy Release Most combustion processes release energy, or heat, for the production of power, for use in industrial processes, and for domestic heating and lighting. Combustion is also a means of producing a desired oxidized product, as in the burning of sulphur to produce sulphur dioxide and ultimately sulphuric acid. In addition, it is a method for disposing of wastes. The energy released by combustion causes a rise of temperature of the products of combustion. The temperature attained depends on the rate of release and dissipation of the energy and the quantity of combustion products.               Fuel Fuel, substance that reacts chemically with another to produce heat, or that produces heat by nuclear processes. The term fuel is generally limited to those substances that burn readily in air or oxygen, emitting large quantities of heat. Fuels are used for heating, for the production of steam for heating and power purposes, for powering internal-combustion engines, and for a direct source of power in jet and rocket propulsion.              Solid Fuels The common solid fuels, in order of heat potential, are coal, coke, wood, sugarcane bagasse, and peat. Combustion of these causes decomposition of the fuel and evolution of the volatile matter as a gas that may burn with a sooty flame. The solid carbonaceous residue burns at a rate determined by the diffusion of oxygen to the surface.               Liquid and Gaseous Fuels Common liquid fuels are fuel oils, gasoline, and naphthas derived from petroleum, and, to a lesser extent, coal tar, alcohol, and benzol obtained from coke manufacture.   Gaseous fuels such as natural gas, refinery gas, and manufactured gases such as producer gas are usually mixed with air before combustion to supply a maximum amount of oxygen to the fuel.  

       Petroleum   Petroleum, or crude oil, naturally occurring oily, bituminous liquid composed of various organic chemicals. It is found in large quantities below the surface of Earth and is used as a fuel and as a raw material in the chemical industry. Modern industrial societies use it primarily to achieve a degree of mobility on land, at sea, and in the air—that was barely imaginable less than 100 years ago. In addition, petroleum and its derivatives are used in the manufacture of medicines and fertilizers, foodstuffs, plastics, building materials, paints, and cloth and to generate electricity.              Composition The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulphur, and trace amounts of metals such as iron, nickel, copper and vanadium. The exact molecular composition varies widely from formation to formation but the proportion of chemical elements vary over fairly narrow limits as follows:   Table: Composition of crude petroleum by weight Element                               Percent range Carbon                                 83 to 87% Hydrogen                            10 to 14% Nytrogen                             0.1 to 2% Oxygen                                0.1 to 1.5% Sulfur                                    0.5 to 6% Metals                                  Less than 1000 ppm               Characteristics The chemical composition of all petroleum is principally hydrocarbons, although a few sulphur-containing and oxygen-containing compounds are usually present; the sulphur content varies from about 0.1 to 5 percent. Petroleum contains gaseous, liquid, and solid elements. The consistency of petroleum varies from liquid as thin as gasoline to liquid so thick that it will barely pour. Small quantities of gaseous compounds are usually dissolved in the liquid; when larger quantities of these compounds are present, the petroleum deposit is associated with a deposit of natural gas.              Formation Petroleum is formed under Earth's surface by the decomposition of marine organisms. The remains of tiny organisms that live in the sea—and, to a lesser extent, those of land organisms that are carried down to the sea in rivers and of plants that grow on the ocean bottoms—are enmeshed with the fine sands and silts that settle to the bottom in quiet sea basins. Such deposits, which are rich in organic materials, become the source rocks for the generation of crude oil. The process began many millions of years ago with the development of abundant life, and it continues to this day. The sediments grow thicker and sink into the seafloor under their own weight. As additional deposits pile up, the pressure on the ones below increases several thousand times, and the temperature rises by several hundred degrees. The mud and sand harden into shale and sandstone; carbonate precipitates and skeletal shells harden into limestone; and the remains of the dead organisms are transformed into more...

      Coal   Coal is a fossil fuel formed in ecosystems where plant remains were preserved by water and mud from oxidization and biodegradation, and by which its chemical and physical properties have been changed as a result of geological action over time, thus sequestering atmospheric carbon. Coal is a readily combustible black or brownish-black rock. It is composed primarily of carbon and hydrogen along with small quantities of other elements, notably sulphur. Coal is extracted from the ground by coal mining, either underground mining or open pit mining (surface mining).It is a nonrenewable resource.          Coal Formation Coal is a sedimentary rock formed from plants that flourished millions of years ago when tropical swamps covered large areas of the world. Lush vegetation, such as early club mosses, horsetails, and enormous ferns, thrived in these swamps. Generations of this vegetation died and settled to the swamp bottom, and over time the organic material lost oxygen and hydrogen, leaving the material with a high percentage of carbon. Layers of mud and sand accumulated over the decomposed plant matter, compressing and hardening the organic material as the sediments deepened. Over millions of years, deepening sediment layers, known as overburden, exerted tremendous heat and pressure on the underlying plant matter, which eventually became coal.               Types of Coal As geological processes apply pressure to dead biotic matter over time, under suitable conditions it is transformed successively into Peat: It is considered to be a precursor of coal, has industrial importance as a fuel in some regions, for example, Ireland and Finland.   Lignite: It also referred to as brown coal, is the lowest rank of coal and used almost exclusively as fuel for electric power generation. Bituminous: It is dense mineral, black but sometimes dark brown, often with well-defined bands of bright and dull material, used primarily as fuel in steam-electric power generation, with substantial quantities also used for heat and power applications in manufacturing and to make coke. Anthracite: It is the highest rank of coal; a harder, glossy, black coal used primarily for residential and commercial space heating.              Coalmine Fires Coalmine fires can be triggered during routine mining operations. For example, sparks generated by mining equipment can ignite explosive gases, coal dust, and even the coal bed itself. Because coal beds provide an almost inexhaustible fuel source, once a coal seam is ignited, it can be extremely difficult to extinguish. The intense heat generated by burning coal can rupture the overlying rock strata, sometimes causing the roof to collapse. Uncontrollable fires in some coal deposits have continued burning for years, posing a danger to local communities..

       Non-Metals   Only eighteen elements in the periodic table are generally considered nonmetals, compared to over eighty metals, but nonmetals make up most of the crust, atmosphere and oceans of the earth. Bulk tissues of living organisms are composed almost entirely of nonmetals. Most nonmetals are monatomic noble gases or form diatomic molecules in their elemental state, unlike metals which (in their elemental state) do not form molecules at all.   Non-metals are basically defined as elements that are not metals. Their physical properties generally include:

They are poor conductors.

They are brittle, not ductile in their solid state.

They show no metallic lustre.

They may be transparent or translucent.

They have low density.

They are gases, liquids, or solids.

Theyform molecules which consists of atoms covalently bonded; the nobel gases are monoatomic.

   Theirchemical properties are generally:

They usually have four to eight valence electrons.

They have high electron affinities, (except noble gases)

They are good oxidizing agents, (except noble gases)

They have hydroxides which are acidic, (except noble gases)

They are electronegative.

           Difference between Metals and Non-Metals Chemical Properties   Metals:

• Usually have 1-3 electrons in their outer shell.
• Lose their valence electrons easily.
• Form oxides that are basic.
• Are good reducing agents.
• Have lower electronegativities.

  Nonmetals:

• Usually have 4-8 electrons in their outer shell.
• Gain or share valence electrons easily.
• Form oxides that are acidic.
• Are good oxidizing agents.
• Have higher electronegativities.

  Physical Properties   Metals:

• Good electrical conductors and heat conductors.
• They are malleable i.e.can be beaten into thin sheets.
• They are ductile i.e.can be stretched into wires.
• Possess metallic lustre.
• Opaque as thin sheet.
• Solid at room temperature (except Hg).

  Nonmetals:

• Poor conductors of heat and electricity.
• They are brittle if a solid.
• They are non-ductile.
• Do not possess metallic lustre.
• Transparent as a thin sheet.
• Solids, liquids or gases at room temperature.

             A substance composed of two or more metals is called: (a) Alloys (b) Metalloids   (c) Non-metals (d) All of these (e) None of these   Answer: (a)            Which one of the following is a metal? (a) Aluminium (b) Gold        (c) Silver (d) All of these (e) None of these   Answer: (d)    

• Metals are good conductor of heat and electricity.
• Non-metals are bad conductor of heat and electricity.
• Metals and non-metals are separated in the periodic table by a diagonal line of elements.
• Metals are malleable and ductile.
• Non-metals are brittle..

      Metals   Metals, group of elements that exhibit all or most of the following physical qualities: they are solid at room temperatures; opaque, except in extremely thin films; good electrical and thermal conductors; lustrous when polished; and have a crystalline structure when in the solid state. Metals and nonmetals are separated in the periodic table by a diagonal line of elements. Elements to the left of this diagonal are metals, and elements to the right are nonmetals. Metallic elements can combine with one another and with certain other elements, either as compounds, as solutions, or as intimate mixtures. A substance composed of two or more metals, or a substance composed of a metal and certain nonmetals such as carbon are called alloys. Alloys of mercury with other metallic elements are known as amalgams.               Physical Properties Metals are generally very strong and resistant to different types of stresses. Though there is considerable variation from one metal to the next, in general metals are marked by such properties as hardness, the resistance to surface deformation or abrasion; tensile strength, the resistance to breakage; elasticity, the ability to return to the original shape after deformation; malleability, the ability to be shaped by hammering; fatigue resistance, the ability to resist repeated stresses; and ductility, the ability to undergo deformation without breaking.             Chemical Properties Metals typically have positive valences in most of their compounds, which means they tend to donate electrons to the atoms to which they bond. Also, metals tend to form basic oxides. Typical nonmetallic elements, such as nitrogen, sulphur, and chlorine, have negative valences in most of their compounds- meaning they tend to accept electrons—and form acidic oxides

       Plastics   Plastics, materials made up of large, organic (carbon-containing) molecules that can be formed into a variety of products. The molecules that compose plastics are long carbon chains give plastics many of their useful properties. In general, materials that are made up of long, chain like molecules are called polymers. Plastics can be made hard as stone, strong as steel, transparent as glass, light as wood, and elastic as rubber. Plastics are also lightweight, waterproof, chemical resistant, and produced in almost any colour. More than 50 families of plastics have been produced, and new types are currently under development.               Uses of Plastics Plastics are indispensable to our modern way of life. The cars we drive, the computers we use, the utensils we cook with, the recreational equipment we play with, and the houses and buildings we live and work in all include important plastic components. The average car contains almost 136 kg (almost 300 Ib) of plastics nearly 12 percent of the vehicle's overall weight. Telephones, textiles, compact discs, paints, plumbing fixtures, boats, and furniture are other domestic products made of plastics. In 1979 the volume of plastics produced in the United States surpassed the volume of domestically produced steel. Plastics are used extensively by many key industries, including the automobile, aerospace, construction, packaging, and electrical industries. The aerospace industry uses plastics to make strategic military parts for missiles, rockets, and aircraft. Plastics are also used in specialized fields, such as the health industry, to make medical instruments, dental fillings, optical lenses, and biocompatible joints.                Types of Plastics A wide variety of both thermoplastics and thermosetting plastics are manufactured. These plastics have a spectrum of properties that are derived from their chemical compositions. As a result, manufactured plastics can be used in applications ranging from contact lenses to jet body components. Thermoplastics: Thermoplastic materials are in high demand because they can be repeatedly softened and remolded. The most commonly manufactured thermoplastics are presented in this section in order of decreasing volume of production.   High-density polyethylene (HDPE) has a density that ranges from 0.94 to 0.97 g/cu.cm (0.62 to 0.64 oz/cu in). HDPE is stiffer, stronger, and less translucent than low-density polyethylene. HDPE is molded into grocery bags, car fuel tanks, packaging, and piping.   Polyvinyl Chloride: Polyvinyl chloride (PVC) is prepared from the organic compound vinyl chloride. PVC is the most widely used of the amorphous plastics. PVC is lightweight, durable, and waterproof. Chlorine atoms bonded to the carbon backbone of its molecules give PVC its hard and flame-resistant properties. In its rigid form, PVC is weather-resistant and is extruded into pipe, house siding, and gutters. Rigid PVC is also blown into clear bottles and is used to form other consumer products, including more...

        Fibres   Fibres are fine hairlike structure of animal, vegetable, mineral or synthetic origin. Commercially available fibres have diameters ranging from less than 0.004 mm (0.00015 in) to 0.2 mm (0.008 in) and they come in several different forms: short fibres (known as staple or chopped), continuous single fibres (monofilament), untwisted bundles of continuous filaments (tow), and twisted bundles of continuous filaments (yarn). Fibres are classified according to their origin, chemical structure or both.                 Animal Fibres All animal fibres are complex proteins. They are resistant to most organic acids and to certain powerful mineral acids such as sulphuric acid (H2SO4). However, protein fibres are damaged by mild alkalies (basic substances) and may be dissolved in strong alkalies such as sodium hydroxide (NaOH).                  Vegetable Fibres Vegetable fibres are predominantly cellulose, which, unlike the protein of animal fibres, resists alkalies. Vegetable fibres resist most organic acids but are destroyed by strong mineral acids. Improper use of most bleaches can also weaken or destroy these fibres. There are four major types of vegetable fibres: seed fibres, which are the soft hairs that surround the seeds of certain plants; bast fibres, the tough fibres that grow between the bark and stem of many dicotyledonous plants; vascular fibres, the tough fibres found in the leaves and stems of mono-cotyledons; and grass-stem fibres. Other fibre types, of limited utility, include strips of leaf skins, such as raffia; the fibre of fruit cases, such as coir; and palm fibres.              Mineral Fibres Glass, which is made from silica sand, is the only inorganic (mineral) fibre widely used in commercial applications. There are two main forms of glass fibres: continuous and staple. Continuous glass fibre, which is made by drawing molten glass into threads, is used in textile materials. The use of air, steam, or gas to disrupt the flow of the molten glass stream produces staple fibres. These fibres can be fabricated into mats or into bulk-molding and sheet-molding compounds with the use of resins, or organic binders. Quartz mineral is high silica, high-purity glass that is good for long-term use at temperatures as high as 1400° C (2552° F).                Synthetic Fibres Synthetic fibres derived from natural cellulose were first developed at the end of the 19th century and became known as rayons. In a typical rayon-making process/natural cellulose made from wood pulp is treated with chemicals to form a thick liquid. This liquid is then extruded as filaments into a weak acid bath that converts the filaments back into pure cellulose. Rayons are not, therefore, completely synthetic but are actually regenerated fibres. more...