Current Affairs 7th Class

PRACTICAL GEOMETRY   FUNDAMENTALS

•           A ruler protractor and compass are used for constructions.
•           Given a line 1 and a point P not on it, a line parallel to 1 can be drawn through the point P, using the idea of 'equal alternate angles' or 'equal corresponding angles'.
•           Students should draw rough sketch before actually constructing the triangle. This is very important for students to get the feel of the triangle.
•           Three independent measurements are required to construct a triangle.
•           The sum of lengths of any two sides of a triangle is greater than its third side»
•           The difference of lengths of any two sides of a triangle is lesser than its third side.
•           The sum of angles in a triangle is\[180{}^\circ \].
•           The exterior angle of a triangle is equal in measure (i.e. is equal to the sum) of interior opposite angles.
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MENSURATION (Perimeter and Area)     FUNDAMENTALS                                                

•          Perimeter is the distance around a closed figure.
•         Area is the part of plane occupied by the closed figure.

(a) Perimeter of a square \[=4\times \] side. Elementary question-1: Find perimeter of a square kabaddi field each of whose side is 20 metres Ans.     Perimeter \[=4\times 20=80\,m\] (b) Perimeter of a rectangle \[=2\times \] (length + breadth) units. (c) Area of a square = (side \[\times \] side). (d) Area of a rectangle = length \[\times \] breadth. Elementary Question-2: Find perimeter and area of a football field whose length and breadth are 40 metres and 70 metres respectively. Ans.     Perimeter  \[=2\times (40+70)=220\,m\] Area \[=40\times 70=2800\text{ }Sq.\text{ }m.\]                                                               (e) Area of a parallelogram = base \[\times \] height sq. units. (f) Area of a triangle \[=\frac{1}{2}\] (Area of the parallelogram generated from it) \[=\frac{1}{2}\times \]base \[\times \] height sq. units

•           Area of a trapezium \[=\frac{1}{2}\,(a+b)\,h\,sq.\] units, where 'a' and 'b' are lengths of parallel sides and 'h' is the height between them.

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SYMMETRY   WHAT IS SYMMETRY?

•          Mathematically, symmetry means that one shape becomes exactly like another when you move it in some way - turn (rotate), flip or slide.
•         Line of symmetry: If a line divides a given figure into two coinciding parts, we say that the figure is symmetrical about the line and the line is called the axis of symmetry or line of symmetry.

For e.g.,                        

•         A line of symmetry is also called a mirror line / mirror symmetry / reflection symmetry.
•         A figure may have no line of symmetry, only one line of symmetry, two lines of symmetry or multiple lines of symmetry.
•        Regular polygons have equal sides and equal angles. They have multiple lines of symmetry.

e.g.,            

•          Each regular polygon has as many lines of symmetry as its sides.
•          A scalene triangle has no line of symmetry.
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SOLID SHAPES     FUNDAMENTALS               

•           Description of Some basic shapes:

(a) Square             It has four sides and four comers, All its sides are of the same length. (b) Rectangle.             It has four sides and four comers. The opposite sides of a rectangle are parallel and of the same length. Every interior angle is a right \[\angle le\].     (c) Triangle           It has three sides and three vertices.   (d) Cuboid It has 6 flat faces, 12 straight edges and 8 vertices.   (e) Cube It has 6 flat faces, 8 vertices and 12 straight edges.   (f) Cylinder           It has 3 faces s\[\to \]1 curved face and 2 flat faces.   (g) Cone           It has 2 faces \[\to \] 1 curved face and 1 flat face. It has 1 curved edge.

•          Two- dimensional shapes have only length and breadth.
•         Three dimensional shapes have length, breadth and height or depth.
•         Three-dimensional (or 3-D) shapes can be visualized on a two dimensional (or 2-D) surface.
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DATA HANDLING AND GRAPHS     FUNDAMENTALS Collection and Tabulation of data:

•          Data obtained in the original form is called a raw data.
•          Data means information in the form of numerical figures
•          Each numerical figure in a data is called an observation.
•          Arranging the data in ascending or descending order is called an array.
•         Arranging the data in a systematic tabular form is called tabulation.
•         The number of times a particular observation occurs is called its frequency.
•         The difference between the highest and the lowest values of the observations in a given data is called its range.
•         When the number of observations is large, we make use of tally marks to find the frequencies.
•         Tallies are usually marked in a bunch of five for ease of counting.
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ALGEBRAIC EXPRESSIONS   ALGEBRAIC EXPRESSION

\[2x\]	Expression
\[2x+y\]	Binomial
\[2x=14\]	Equation

 

•                  Variable: A symbol which takes various values is known as a variable. Normally it is denoted by x, y, z etc.
•                   Algebraic expression: A combination of constants and variables connected by some or all of the four fundamental operations \[+,\] \[-,\]\[\times \]and \[\div \] is called an algebraic expression.

e.g., \[-5x+6\]is an algebraic expression.

•                   Here \[-5\]is the coefficient of the variable 'x' and 6 is the constant.

  Various types of algebraic expression: (a) Monomial: An algebraic expression which contains only one term, is called as monomial. Thus, \[2x,\] \[3y,\] \[5xy,\] \[6a{{b}^{2}},\] \[-11\] etc. are called monomials. more...

EXPONENT AND POWERS   POWER \[\frac{{{a}^{m}}}{{{a}^{n}}}={{a}^{m}}-n\] \[{{5}^{3}}\div {{5}^{2}}={{5}^{3}}-2\]   FUNDAMENTALS

•                   Exponential form is nothing but repeated multiplication.

There are two part of an exponent. Exponent\[\to \]base, Power/ Index                                                             Example:            

•                   Base denotes the number to be multiplied and the power denotes the number of times the base is to be multiplied.

\[a\times a\times a={{a}^{3}}\](read as 'a' cubed or 'a' raised to the power 3) \[a\times a\times a\times a\times a\times a={{a}^{6}}\](read as 'a raised to the power 6 or 6th power of a)             ................................................................................... \[a\times a\times a\].......(n factors) \[={{a}^{n}}\] (read as 'a' raise to the power n or nth power of a)

•                    (a) When a negative number is raised to an even power the value is always positive.

e.g., \[{{\left( -5 \right)}^{6}}=\left( -5 \right)\times \left( -5 \right)\times \left( -5 \right)\times \left( -5 \right)\times \left( -5 \right)\times \left( -5 \right)\]\[=15625\] (b) When a negative number is raised to an odd power, the value is always negative. e.g., \[{{\left( -3 \right)}^{5}}=\left( -3 \right)\times \left( -3 \right)\times \left( -3 \right)\times \left( -3 \right)\times \left( -3 \right)=\left( -243 \right)\] Note:    (a) \[{{(-1)}^{odd\,\,number}}=-1\] (b) \[{{(-1)}^{even\,\,number}}=+1\]   more...

Nutrition   Nutrition in Plants All living beings need food to carry out various life processes. Food gives living beings the material to build and maintain their body. Nutrition is the process by which an organism obtains its food and utilize them. The nutrition can be categorised mainly into two type's namely autotrophic and heterotrophic nutrition.   Autotrophic Nutrition Autotrophic organisms make their own food from simple raw materials available in their environment. Green plants, algae and some bacteria can produce their own food by the process of photosynthesis. The process of photosynthesis occurs only when plants or algae or some bacteria have green pigment, called chlorophyll in their cells. In the process of photosynthesis, the leaves of plants convert water and carbon dioxide into glucose or sugar and oxygen with the help of energy from the sun. Plants take in carbon dioxide from air and water from the soil.   Heterotrophic Nutrition The plants which do not contain chlorophyll obtain their food by heterotrophic mode of nutrition. There are mainly three types of plants which obtain their food by heterotrophic nutrition. These plants are:   Saprophytic plants Saprophytes are the non-green plants that feed on dead and decaying organic matters derived from plants and animals. These organisms break down the organic matters by secreting digestive juices into it. For example, mushrooms and toadstool, etc.     Parasitic plants Some non-green plants live inside or on other organisms and derive nutrition from them. Such plants are called parasites and the organisms on which the parasite lives are called hosts. For example, dodder is a parasitic plant that winds its yellowish and threadlike stems around other plants and draw nutrition from them.     Insectivorous plants Some plants obtain a part of their food from insects. For example pitcher plants trap the insects in their modified leaf, kill them and digest them to obtain nutrients. In fact insectivorous plants grow in the soil which is not very rich in nutrients. So they get essential nutrients by eating insects.                      Nutrition in Animals Animals cannot make their own food because they do not have green pigment named chlorophyll. Animals depend on plants or other animals for their food.   Nutrition in Animals involve Five Steps Ingestion: Intake of food inside the body is called ingestion. Digestion: Breaking down of large food molecules to smaller one is called digestion. Absorption: The digested food is absorbed into blood stream through intestinal wall. This process is known as absorption. Assimilation: The process of utilizing absorbed food by body cells for various metabolic processes is called assimilation. Egestion: The process of removing undigested food out more...

Fibre to Fabric   Fibre Fibre is a long and thin strand of a material. It can be categorised into two type’s namely natural fibre and manmade fibre.   Natural Fibre Natural fibre is derived from plants and animals. Fibres such as cotton, flax and jute are derived from plants. Fibres such as silk and wool are derived from animals.   Plant Fibres The fibres which we get from plants are called plant fibres. Cotton, flax and jute are plant fibres. Cotton: Cotton fibre is obtained from the seeds of the cotton plant. Flax: Flax fibre is soft, lustrous and flexible. It is stronger than cotton fibre but is less elastic. The finer grade of flax fibre is used for producing linen fabrics such as damasks, Lace and sheeting. The coarser grades of flax fibre are used for manufacturing twine and rope. Flax fibre also forms the raw material for high quality paper industry. Jute: Jute is a long, rough and shiny fibre. It is spun into coarse and strong threads. Jute the cheapest natural fibre. It is composed of plant materials such as cellulose, lignin and pectin.   Animal Fibres The fibres which we get from animals are called animal fibres. Wool and silk are animal fibres. Silk: Silk is derived from cocoons of silkworm. Silkworms are reared for obtaining silk. This is known as sericulture. The various silk fabrics are crepe, satin, damask, taffeta, etc. Clothes made from silk fibre are soft, lustrous and comfortable to wear. Wool: Wool is obtained by cutting the fleece from the body of some hairy animals such as sheep, goat, yak and camel. The main source of wool is sheep. Wool is used for making warm clothes.   Man Made Fibres Man-made fibres can be divided into two type’s namely regenerated fibres and synthetic fibres. Rayon and acetate are two regenerated fibres. Nylon, polyester, acrylic, etc. are synthetic fibres.   Regenerated Fibres The regenerated fibres are made from natural materials and the material is processed to form the fibre structure. Regenerated fibres are derived from the cellulose found in cotton and wood pulp. Acetate: Acetate is a weak fibre, but fibres of different diameters can be produced. Acetate fibre produces luxurious fabrics that look similar to silk. The fabric made from this fibre is wrinkle free, pliable and soft with a good drape. Rayon: Rayon is strong and extremely absorbent. Rayon fibre does not melt but burns at high temperature. Fabric made from rayon wrinkle easily and may stretch when wet and shrink when washed.             Synthetic Fibres Synthetic fibres are completely made from chemicals. These fibres are stronger than natural or regenerated fibres. Both synthetic and regenerated acetate fibres are thermoplastic, which means they are softened by heat. Synthetic fibres melt at very high temperature.   Acrylic Fibre: Acrylic fibre or acrylonitrile is made from natural gas and petroleum. The fabric made from acrylic fibre is soft and luxurious. Acrylic fibre is very sensitive to more...

Physical and Chemical Changes Heat Heat is a form of energy and energy is the capacity to do work. This clearly indicates that work can be done with the help of heat.   Temperature The decree of hotness and coldness is called the temperature of the body. The two common scales that are used to measure the temperature of the body are Celsius scale and Fahrenheit scale. On the Celsius scale, the melting point of ice is and boiling point of water is On the Fahrenheit scale, the melting point of ice is  and boiling point of water is   Thermometer  

• A thermometer is a device for measuring the temperature of an object. There are two common types of thermometers: Laboratory thermometer and Clinical thermometer. Both of these thermometers are based on Celsius scale of temperature.
• The range of a laboratory thermometer is generally from  to.
• The range of Clinical thermometer is from  to 

    Effects of Heat Heat brings tremendous changes in objects by acting on it. Heat causes the following changes: Contraction and Expansion of Substances: All substances, whether solid, liquid or gas expand on heating and contract on cooling. On heating gases expand the most, the liquids expand less than gases and solids expand the least. You must have observed the electric wire on the street poles which becomes loose in summer and tight in winter. This happens just because of the effect of heat. Change in State: Solid changes into liquid on heating and liquid changes into gas on further heating. For example, ice changes into water and water changes into vapour. On the other hand, when vapour cools, it changes into liquid and when liquid cools, it changes into solid.   Flow of Heat Heat can flow through solids, liquids, gases and even through vacuum. Heat can flow through three ways namely: conduction, convection and radiation. Conduction: The flow of heat from hotter part of a body to colder part of the body. When two bodies are in contact is called conduction. The transfer of heat from one body" to another is stopped when both the bodies acquire same temperature. Convection: Liquids and gases are poor conductors of heat. Heat travels in liquids and gases by the process called convection. In the process of convection, heat travels in liquid and gas by the displacement of liquid or gas. Radiation: In addition to travelling through solid, liquid or gas, more...