Current Affairs 8th Class

  Coal and Petroleum   Coal Coal is a combustible sedimentary rock. It is a fossil fuel. It is composed primarily of carbon and hydrogen along with small quantities of other elements, notably sulphur. It is a nonrenewable resource.   Coal Formation                                                                   Coal is a sedimentary rock formed from plants that flourished millions of years (about 300 million) 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                                                                Peat               Lignite     Bituminous    Anthracite   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 is also referred as brown coal, is the lowest rank of coal and used almost exclusively as fuel for electric power generation. Bituminous: It is dense rock which is usually black but sometimes dark brown, 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 give some other use.   Petroleum It is naturally occurring liquid. It is, also known as crude oil, a fossil fuel, formed over a period of millions of years, from organisms that lived in the sea at that time. Their dead bodies sank to the bottom of sea and were covered with mud and sand. Due to high pressure, heat, in the absence of air, the dead remains of tiny plants and animals were slowly converted into petroleum. The process of separating crude petroleum oil into more useful fractions is called refining. The various useful fractions obtained by the refining of petroleum are: Petroleum gas. Petrol, Kerosene, Diesel, Lubricating oil. Paraffin wax and bitumen.   Combustion It is a process of rapid oxidation or burning of a substance in the presence of oxygen to produce heat and light. Requirements for the occurrence of combustion are:
  • Presence of combustible substance
  • Presence of supporter of combustion (like air or oxygen).
  • Heating the combustible substance to its ignition temperature.
Fuel Fuel, substance that reacts chemically with another more...

  Conservation of Plants and Animals   Conservation It is the protection of natural resources like plants, animals, soil, water, fossil fuels etc. and the sustainable use of such resources. Natural resources are grouped into two categories: renewable resource is the one that may be replaced over the time by natural processes such as fish populations, natural vegetation or is inexhaustible such as the solar energy. Nonrenewable resources are those which are limited in supply and cannot be replaced even over extremely long period of time. The nonrenewable resources include fossil fuels and mineral deposits, such as iron ore and gold ore. Conservational activities for the nonrenewable resources focus on maintaining an adequate supply of these resources well in the future.                 Natural resources are conserved for their biological, economical and recreational values, as well as their natural beauty and importance to the local cultures. For example, tropical rainforests are protected for their important role in both the global ecology and the economic livelihood of the local culture. A coral reef may be protected for its recreational value for scuba divers and a scenic river may be protected for its natural beauty.   Biodiversity A wild range of different types of organisms which grow, multiply and thrive naturally, are found at any given time in a particular habitat. We should conserve forests and wildlife to preserve biodiversity to prevent endangered species from becoming extinct and to maintain ecological balance in nature.   Deforestation     Deforestation means large scale removal of forest prior to its replacement by other land uses Forests are removed for a variety of reasons, including agriculture, timber harvesting, mining and to make way for roads, dams and human settlements.   Protected Areas Protected areas are the areas of land or sea especially dedicated to the protection and maintenance of biodiversity. These are managed through legal means and have been set up within the legal frame work of Indian wildlife (Protection) Act.1972. Examples of protected areas are national parks and wildlife sanctuaries.   National Parks A national park is a large area dedicated to conserve the environment, natural resources and the wildlife therein. In a national park,
  • Private rights are non-existent.
  • Forestry operations, grazing of animals and hunting of animals are prohibited.
  • Visitors are allowed to enter only for study, cultural and re-creative purposes.
  • Exploitation of habitat or wildlife is banned.
  Wildlife Sanctuaries
  • A wildlife sanctuary is similar to a national park. However, it aims only at conservation of species. The wildlife sanctuaries have the following features:
  • The boundary of a sanctuary is not limited by state legislation.
  • The killing, hunting or capturing of any species is prohibited.
  • Private ownership may be allowed to continue in a sanctuary.
  • Forestry and other usages may be permitted, but to the extent that they do not affect wildlife adversely.
  Forest Reserves These more...

  Cell Structure and Functions   Cell Structure Cells are of two Types prokaryotic cell and eukaryotic cell, found only in bacteria and archaebacteria, all the components, including the DNA, mingle freely in the cell's interior, a single compartment. Eukaryotic cells, which make up the plants, animals, fungi and all other life forms contain numerous compartments or organelles within each cell. The DNA in eukaryotic cells is enclosed in a special organelle called the nucleus, which serves as the cell's command centre and information library. The term prokaryote comes from Greek word that mean “before nucleus” or “prenucleus,” while eukaryote means "true nucleus."   Prokaryotic Cells Prokaryotic cells are among the thinnest of all cells, ranging in size from 0.0001 to 0.003mm in diameter. These cells, which can be rodlike, spherical or spiral in shape are surrounded by a protective cell wall.     Eukaryotic Cells Eukaryotic cells are typically about ten times larger than the prokaryotic cells. In animal cells, the plasma membrane rather than a cell wall, forms the cell's outer boundary. With a design similar to the plasma membrane of prokaryotic cells, it separates the cell from its surroundings and regulates the traffic across the membrane.    The eukaryotic cell cytoplasm is similar to that of the prokaryotic cell except for one major difference. Eukaryotic cells have a nucleus and numerous other membrane enclosed organelles. Like separate rooms of a house, these organelles enable specialized function to be carried out efficiently. For example, the building of proteins and lipids take place in separate organelles where specialized enzymes geared for each job are located. The nucleus is the largest organelle in an animal cell. It contains numerous strands of DNA the length of each strand being many times the diameter of the cell. Unlike the circular prokaryotic DNA, long sections of eukaryotic DNA pack into the nucleus by wrapping around proteins. As a cell begins to divide, each DNA strand folds over onto itself several times, forming a rod-shaped chromosome.   Cell Functions To stay alive, cells must be able to carry out a variety of functions. Some cells must be able to move and most cells must be able to divide. All cells must maintain the right concentration of chemicals in their cytoplasm, ingest food and use it for energy, recycle molecules, expel wastes and construct proteins. Cells must also be able to respond to ranges in their environment.   Movement Many unicellular organisms swim, glide, thrash or crawl in search for food and escape from enemies. Swimming organisms often move by means of a flagellum, a long tail-like structure made of protein. For example, many bacteria have one, two or many flagella that rotate like propellers to drive the organism along. Some single-celled eukaryotic organisms such as euglena also have a flagellum, but it is longer and thicker than the prokaryotic flagellum. The eukaryotic flagellum works more...

  Reproduction and Adolescence   Reproduction Reproduction is a biological process by which new individual organism-off springs-are produced from their parents. Reproduction is one of the essential functions of plants, animals and other organisms for the preservation of the species. In almost all animals, reproduction occurs during or after the period of maximum growth.   Types of Reproduction Asexual Reproduction It is a type of reproduction by which offspring arise from a single organism and it does not involve the fusion of gametes.   Types of Asexual Reproduction Binary fission - in this type of reproduction the fully grown parent cell splits into two halves, producing two new cells. For example, amoeba and paramecium.     Binary fission in Amoeba  
  • Budding - in this type of reproduction, from the parent organism a bulb-like projection called bud arises which grows and eventually break away from the parent. For example, hydra and yeast.
    Budding In Yeast   Vegetative Propagation - is found in plants where new independent individuals are formed without the production of seeds and spores. For example, propagation through leaves in Kalanchoe, Bryophyllum.   Vegetative propagation by leaves in Bryophyllum   Spore Formation - is found in nonflowering plants such as fungi and bacteria. In this method, the plant produces hundreds of tiny spores which can grow into new plants. Spore formation in Rhizopus   Fragmentation - in this method a new organisms grows from a fragment of the parent. Each fragment develops into a mature, fully grown individual. For example, lichens, liverworts.   Fragmentation in Spirogyra   Sexual Reproduction It is a method of reproduction of producing a new individual from two parents by combining their genetic information. For example, human beings, dog, cat, etc.   Fertilisation The process of formation of zygote by the fusion of male gamete and female gamete is known as fertilisation. There are two types of fertilization: internal and external fertilisation.     Fertilisation in humans to form a zygote (fertilised egg)  
  • External fertilization - this type of fertilization occurs outside the animals body. For example, starfish, jellyfish, etc.
  • Internal fertilization - this type of fertilization occurs inside the animals body. For example, birds, reptiles, mammals, etc.
  Gametes Gametes are the cells involved in sexual reproduction. In humans male reproductive organ is testes and female reproductive organ is ovaries. Male gamete in animals is called sperm and the female gamete in animals is called egg.   Zygote The new cell which is formed by the fusion of male and female gamete is called zygote.   Adolescence and Puberty Adolescence, the period of transition between childhood more...

  Force, Friction and sound   Force A force is a push or pull. The direction in which an object is pussed or pulled is called the direction of the force. Whenever there is an interaction between two objects, there is a force acting on each of the objects. Forces acting between objects can be placed into two categories:   Contact Forces Are those types of forces which result when the two interacting objects are perceived to be physically contacting each other.   Types of Contact Forces
  • Muscular Force - is the force exerted by the muscles of the body. This force can be applied to an object only when our body is in contact with the object, therefore muscular force is a contact force.
  • Frictional Force - is the force which opposes the motion of one body over another body.
  Non-contact Forces Are those forces which result when the two interacting objects are not in physical contact with each other.   Types of Non-contact Forces
  • Gravitational Force - is the force by which all things with mass are brought toward one another. It is the gravitational force between the sun and the earth which holds the earth in its orbit around the sun.
  • Magnetic Force - is the force exerted by a magnet. The magnetic force between two magnets placed near one another can be that of "attraction" or "repulsion” depending upon which poles of the two magnets are facing each other.
  • Electrostatic Force - is the force exerted by an electrically charged object.
  Pressure Pressure, in mechanics is the force per unit area exerted by a liquid or gas on a body surface, with the force acting at right angles to the surface uniformly in all directions. Mathematically: p = Where P is the pressure, F is the normal force and A is the area. Unit of pressure is Pascal or\[N/{{m}^{2}}\]   Atmospheric Pressure This pressure exerted by the atmosphere is called atmospheric pressure. It decreases with increase in height.   Friction Friction is the force that opposes the motion of an object when the object is in contact with another object or surface. Friction results from two surfaces rubbing against each other or moving relative to one another. It can hinder the motion of an object or prevent an object from moving at all. The strength of frictional force depends on the nature of the surfaces that are in contact and the force pushing them together.   Causes of Friction Friction occurs because rough surfaces tend to catch on one another as they slide past each other. Even surfaces that are apparently smooth can be rough at the microscopic level. They have many ridges and grooves. The ridges of each surface can get stuck in the grooves of the other, effectively creating a type of mechanical bond or glue, between the surfaces.   Kinds of Friction
  • Static Friction - the frictional force acting between the two more...

  Chemical Effects of Current and Light   Chemical reactions are caused by passing of electric current through a conducting solution. This is called chemical effect of electric current.   Electric Current An electric current is a movement of charge. When two objects with different charges come in contact with each other and redistribute their charges, an electric current flows from one object to the other until the charge is distributed according to the capacities of the objects. If two objects are connected by a material that lets charge flow easily, such as a copper wire, then an electric current flows from one object to the other through the wire. Electric current is measured in ampere.   Conduction of Electric Current Through Liquids A solution of a substance or a substance in a liquid state which can conduct electricity is called an electrolyte. Most liquids that conduct electricity are solutions of acids, bases and salts. The Chemical decomposition of an electrolyte on passing an electric current through it is called electrolysis. Electrolysis is used very widely in industries like electroplating of metals, refining of copper and extraction of aluminum from ore. To make electrolysis happen there require two conductors cathode (-) and anode (+).     Electroplating The process of covering a more reactive metal with a less reactive metal with the help of electricity is known as electroplating. Material to be plated should be connected as cathode while anode usually loses material.   Light The sense of sight is one of the most important senses. Through this we see things around as. Light is an electromagnetic radiation, specifically radiation of a wavelength that is visible to the human eye.   Luminous and Non-luminous Objects
  • The objects which emit their own light are called luminous objects. For example, sun, stars, electric bulb, glowing tube light, torch, etc.
  • The objects which do not emit their own light are called non-luminous objects. For example, the moon, earth, table, chair, book, trees, etc.
  Reflection of Light Is the phenomenon of sending back light rays which fall on the surface of an object.     Laws of reflection According to first law of reflection: the incident ray, the reflected ray and the normal ray, all lie in the same plane. According to second law of reflection: the angle of incidence is always equal to angle of reflection.   Periscope Is a long, tubular device used to observe over, around or through an object that is out of direct line of sight. A periscope works on the reflection of light from two plane mirrors arranged parallel to one another.   Human Eye The eye enables us to see the various objects around us. The main parts of human eye are:  
  • Cornea - is the front part of the eye which is made more...

  Solar System and Some Natural Phenomenon   Solar System Solar system, the sun and everything that orbits the sun, including the planets and their satellites the dwarf plants, asteroids, kuiper belt objects and comets.     Sun Solar is the closest star to the earth. Its average distance from the earth is about 150 million kilometers. It consists mainly of hydrogen and helium. Diameter of sun is about 1.4million km. The temperature at its surface is about\[6000{}^\circ C\].   Planets Based on the distances of planets from the sun they are as follows: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. All the planets revolve around the sun in a fixed path called orbit. Planets which are close to the sun like Mercury, Venus, Earth and Mars are called inner planets or terrestrial planets. Jupiter, Saturn, Uranus and Mars are known as the outer planets or jovian planets as they are far from the sun.
  • Mercury- is nearest to the sun. This planet has a rocky surface which is covered with craters. It is the smallest planet of the solar system.
 
  • Venus- is the second planet from the sun. Venus is a rocky planet. It is the hottest planets as its atmosphere is mainly made up of carbon dioxide. It rotates on its axis from east to west.
 
  • Earth - is the third planet from the sun. Earth's atmosphere has sufficient oxygen, the gas we need to live and water.
 
  • Mars - is also known as a red planet. The thin atmosphere of mars contains mainly carbon dioxide with small amounts of nitrogen, oxygen, noble gases and water vapour. It appears red due to the high amount of iron oxide present on its surface.
 
  • Jupiter - is the biggest planet and is made mainly of hydrogen and helium.
 
  • Saturn - is the second biggest planet of the solar system and is made up of mainly hydrogen and helium. It has well developed system of rings surrounding it. It is the least dense planet and can float in water.
  • Uranus - is the third biggest planet of the solar system and is mainly made up of hydrogen and helium.
 
  • Neptune - is the outermost planet of the solar system and is made mainly of liquid and frozen hydrogen and helium gases.
The Moon A celestial body that revolves around a planet is known as natural satellite or moon of the planet. The earth has only one moon. It reflects the light of the sun. Its surface is covered with craters and mountains.    Phases of moon Shapes of the bright part of the moon, as seen from the earth, are known as the phases of moon.     Constellations Are group of stars which appear to form some recognizable more...

  Pollution of Air and Water   Pollution Our environment is our surrounding. It comprises all living and nonliving things. Any undesirable change in the physical, chemical or biological characters of air, water and soil leads to environmental pollution which is harmful to human beings directly or indirectly.   Pollutant A pollutant is a substance that may be added to the environment directly or indirectly by man or natural events, to an extent which adversely affects humans, animals, vegetation and other materials.   Air Pollution Air pollution is defined as the addition of undesirable materials into the atmosphere either due to human activities which adversely affect the quality of the air and hence life on earth or through natural process like volcanic eruption.   Causes of Air Pollution  
1. Human activities 2. Thermal power plants
3. Burning of fossil fuels 4. Motor vehicles
5. Industries 6. Volcanic eruption
  Greenhouse Effect Greenhouse effect may be defined as a phenomenon that enables the earth's atmosphere to trap the heat from the sun and prevent it from escaping into the outer space, there by warming the earth's surface.   Acid Rain The burning of fossil fuels containing sulphur, nitrogen and carbon produces acidic oxides of these elements. Carbon dioxide, an oxide of carbon, dissolves in water droplets to produce carbonic acid (a weak acid). The oxides of sulphur and nitrogen react with water to form sulphuric acid more...

  Number System and Operations   In Mathematics we frequently come across different types of numbers. The different types of numbers are natural numbers, whole numbers, rational numbers, integers, irrational numbers, and real numbers. The natural number starts form 1 and goes to infinity Thus we can say that all the positive real numbers starting from 1 are called natural numbers. The whole numbers are all counting numbers together with 0. The set of all natural numbers, 0 and negative of all natural numbers including 0 are called integers. The rational numbers are the numbers which can be written in the form of\[\frac{p}{q}\], where p and q are integers and\[q\ne 0\].   Properties of Rational Number Rational numbers satisfy various properties which are given below:   Closure Property When we add two rational numbers the result is also a rational number, i.e. rational numbers are closed under addition. For example, \[\frac{3}{4}+\frac{8}{9}=\frac{59}{36}\] which is also a rational number.
  • The difference between two rational numbers is also a rational number. example, \[\frac{8}{9}-\frac{5}{6}=\frac{1}{18}\]
  • Multiplication and division of two rational numbers are not necessarily a rational number.
  Commutative Property The two rational numbers can be added in any order, the result in both cases will be same. Hence we can say that addition of two rational numbers is commutative. \[\frac{2}{3}+\frac{5}{6}=\frac{5}{6}+\frac{2}{3}=\frac{9}{6}\].
  • This is called the commutative property of addition.
  • Subtraction is not commutative for rational numbers.
  • Multiplication is commutative for rational numbers i.e. for any two rational numbers \[x,\]and\[y,\]\[X\times Y=Y\times X\].
  • Division is not commutative for rational numbers.
  Associative Property
  • Addition is associative for rational numbers i.e. for any three rational number \[x,\]\[y\] and \[z,\]\[x+(y+z)=(x+y)+z\]
  • Subtraction is not associative for rational numbers.
  • Multiplication is associative for rational numbers i.e. for any three rational numbers \[x,\]\[y\] and\[z,\]\[x\times (y\times z)=(x\times y)\times z\].
  • Division is not associative for rational numbers.
  Distributive Property For all rational numbers x, y and z, we have:
  • \[x(y+z)=xy+xz\]
  • \[x(y-z)=xy-xz\]
  Rules of Divisibility
  • 2 is a factor of all numbers whose unit digit can be divided by 2.
  • 3 is a factor if the sum of digits can be divided by 3.
  • 4 is a factor if the number composed of the last two digits cam be divided by 4.
  • 5 is a factor if the last digit be either 0 or 5.
  • 6 is a factor if both 2 and 3 are factors.
  • 8 is a factor if the last three digits of a number can be divided by 8.
  • 9 is a factor if the sum of digits can be divided by 9.
11 is a factor if the difference between the sum of the alternative digits of the number is 0 or divided by 11.  

  Exponents   Exponents Any number of the form \[{{x}^{n}},\]where n is a natural number and 'x' is a real number is called the exponents. Here n is called the power of the number x. Here x is the base and n is exponent (or index or power). Power may be positive or negative. For any rational number\[{{\left( \frac{x}{y} \right)}^{n}},\]n is called the power of the rational number. So,\[{{\left( \frac{x}{y} \right)}^{n}}=\frac{{{x}^{n}}}{{{y}^{n}}}=\frac{x}{y}\times \frac{x}{y}\times \frac{x}{y}\times \frac{x}{y}\times \frac{x}{y}\times -----\times \frac{x}{y}\](n times)   Uses of Exponents The exponents can be used for various purposes such as comparing large and small numbers, expressing large and small numbers in the standard forms. It is used to express the distance between any two celestial bodies which cannot be expressed in the form of normal denotation. It is also useful in writing the numbers in scientific notation. The size of the microorganisms is very-very small and it cannot be written in normal denotation and can easily be expressed in exponential form.   Radicals Expressed with Exponents Radicals are the fractional exponents of any number. Index of the radical becomes the denominator of the fractional power. \[n\sqrt{a}=\frac{1}{{{a}^{n}}}\]or, \[\sqrt{9}=\sqrt[2]{9}=\frac{1}{{{9}^{2}}}=3\] Let us convert the radicals to exponential expressions, and then apply laws of exponent to combine the terms. For example: \[\sqrt[3]{2}\,\sqrt[4]{2}={{2}^{\frac{1}{3}}}\,{{2}^{\frac{1}{4}}}={{2}^{\frac{1}{3}+}}^{\frac{1}{4}}={{2}^{\frac{7}{12}}}=\sqrt[12]{{{2}^{7}}}\]
  • Example: Simplify:\[\frac{\sqrt{5}}{\sqrt[3]{5}}\]
(a) \[{{5}^{1/3}}\]                             (b) \[{{5}^{1/5}}\]        (c) \[{{5}^{1/6}}\]                              (d) \[{{5}^{3/8}}\] (e) None of these Answer (c)   Explanation: \[\frac{{{5}^{\frac{1}{2}}}}{{{5}^{\frac{1}{3}}}}={{5}^{\frac{1}{2}-\frac{1}{3}}}={{5}^{\frac{1}{6}}}\]  
  • Example: \[\frac{{{2}^{4}}}{3}\]is equal to:
(a) \[\frac{4}{9}\]                                   (b) \[\frac{16}{81}\] (c)\[\frac{32}{27}\]                                  (d) \[\frac{8}{81}\] (e) None of these Answer (b)   Explanation: \[{{\left( \frac{2}{3} \right)}^{4}}=\left( \frac{2}{3} \right)\times \left( \frac{2}{3} \right)\times \left( \frac{2}{3} \right)\times \left( \frac{2}{3} \right)=\frac{2\times 2\times 2\times 2}{3\times 3\times 3\times 3}\]\[=\frac{{{2}^{4}}}{{{3}^{4}}}=\frac{16}{81}\]   Squares and Square Roots A number x is called a square number if it can be expressed in the form \[{{y}^{2}},\] here y is called the square root of x. Symbol used for square root is\[\sqrt{{}}\].   Properties of square Numbers
  • Every square number can be expressed as the sum of odd natural numbers.
  • Square Number can only end with digits 0, 1, 4, 5, 6 and 9.
  • If the last digit of a number is 0, its square ends with 00 and the preceding digits must also form a square.
  • If the last digit of a number is 1 or 9, its square ends with 1 and the number formed by its preceding digits must be divisible by four.
  • If the last digit of a number is 2 or 8, its square ends with 4 and the preceding digits must be even.
  • If the last digit of a number is 3 or 7, its square ends with 9 and the number formed by its preceding digits must be divisible by four.
  • If the last digit of a number is 4 or 6, its square ends with 6 and the preceding digits must be odd.
  • If the last digit of a number is 5, its square ends with 5 and the preceding digits must be 2.
  • A square more...


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