# Current Affairs 6th Class

#### Notes - Data Handling

Data Handling   In this chapter we will learn about pictograph and bar graph.   Data Data is a collection of facts, such as numbers, observations, words or even description things.   Observation Each numerical figure in a data is called observation.   Frequency The number of times a particular observation occurs is called its frequency.   Statistical Graph The information provided by a numerical frequency distribution is easy to understand when we represent it in terms of diagrams or graphs. To represent statistical data, we use different types of diagrams or graphs. Some of them are:   (i)  Pictograph (ii) Bar graph   Pictograph A pictograph represents the given data through pictures of objects. It helps to answer the questions on the data at a glance.   Example: The following pictograph, shows the number of cakes sold at a bakery over five days.
 Day Number of cakes = 10 cakes Monday Tuesday Wednesday Thursday Friday
Based on above pictograph, answer the following questions:   (i)  On which day, the maximum number of cakes were sold? (a) Monday                    (b) Tuesday       (c) Wednesday                (d) Friday (e) None of these   Answer (a) Explanation: Clearly from the pictograph, we can say that on Monday the maximum number of cakes were sold.   (ii) How many total number of cakes were sold over more...

#### Notes - Mensuration

Mensuration   Perimeter and Area of Plane Figures Perimeter of geometrical figure is the sum of its sides. There are different types of geometrical figures. Figures are classified by their shapes and sizes. Area of a geometrical figure is its total surface area.   Perimeter and Area of a Triangle Ø  Perimeter of a triangle = Sum of the length of all sides. Ø  Area of a right triangle $\text{=}\frac{\text{1}}{\text{2}}\times \text{Base}\times \text{Height}$ Ø  Perimeter of an equilateral triangle $\text{=3}\times \text{Side}$ Ø  Area of an equilateral triangle $\text{=}\frac{\sqrt{\text{3}}}{\text{4}}\times {{\text{(Side)}}^{\text{2}}}$   Perimeter and Area of a Parallelogram Parallelogram is a quadrilateral whose opposite sides are equal and parallel to each other. In the given figure ABCD is a Parallelogram in which $\text{AB}\parallel \text{CD,}\,\,\text{BC}\parallel \text{AD,}\,\,\text{AB}=\text{CD}$ and $\text{AD=BC}$     Perimeter of a Parallelogram = 2 (sum of two adjacent sides) Hence, perimeter of a parallelogram $\text{ABCD=2(AB+BC)}$Area of a parallelogram = Base $\text{ }\!\!\times\!\!\text{ }$ Height Therefore, the area of a parallelogram $\text{ABCD=AB }\!\!\times\!\!\text{ CE}$   Perimeter and Area of a Rectangle A rectangle has four right angles and its opposite sides are equal. Longer side of a rectangle is called length and shorter side is called width.     Perimeter of rectangle  $ABCD=AB+BC+CD+DA$ = length + width + length + width = 2(length + width) Hence, perimeter of a rectangle = 2(length + width) Area of a rectangle = length $\times$width   Perimeter and Area of a Rhombus A rhombus is a parallelogram with four equal sides. Therefore, perimeter of rhombus$=4\times side$. In the figure given below ABCD is a rhombus.   Perimeter of a rhombus, $=4\times side$ Area of a rhombus = base $\times$ height Also area of a rhombus $\text{=}\frac{1}{2}\times$ product of length of diagonals. Perimeter and Area of a Square A square has four equal sides and each angle of$90{}^\circ$. In the picture given below, ABCD is a square because its all sides are equal and each angle is a right angle.     Perimeter of square = side + side + side + side$=4\times side$ Area of a Square = side $\times$side = ${{(side)}^{2}}$   Perimeter and Area of a Trapezium A quadrilateral whose one pair of sides are parallel is called a trapezium. The given figure is a trapezium in which parallel sides are AB and CD and non-parallel sides are AD and BC     Perimeter of a trapezium = Sum of the length of all sides Area of a trapezium $=\frac{1}{2}\times$ (Sum of lengths of parallel sides) $\times$distance between parallel sides.   Cirumference and Area of a circle A round plane figure whose all points are equidistant from a fixe point is more...

#### Notes - Geometry and Symmetry

Geometry and Symmetry   Basic Geometrical Shapes Lines and angles are the main geometrical concept and every geometrical figure is made up of lines and angles. Triangles are also constructed by using lines and angles.   Point A geometrical figure which indicates position but not the dimension is called a point. A point does not have length, breadth and height. A point is a fine dot. P is a point on a plane of paper as shown below.     Line A set of points which can be extended infinitely in both directions is called a line.     Line Segment A line of fix length is called a line segment.     In the above figure RS is a line segment and the length of RS is fixed.   Ray A ray is defined as the line that can be extended infinitely in one direction.     In the above figure AB can be extended towards the direction of B. Hence, called a ray.   Note: A line segment has two end points, a ray has only one end point and a line has no end points.   Angle Angle is formed between two rays which have a common point.     Vertex or common end point is O. OA and OB are the arms of $\angle AOB$ The name of the above angle can be given as $\angle AOB$or $\angle BOA$ The unit of measurement of an angle is degree$({}^\circ )$   Types of Angles Acute Angle The angle between $0{}^\circ$ and $90{}^\circ$ is called an acute angle. For example, $10{}^\circ ,\,\,30{}^\circ ,\,\,60{}^\circ ,\,\,80{}^\circ$are acute angles.   Right Angle An angle of measure $90{}^\circ$ is called a right angle.   Obtuse Angle An angle whose measure is between $90{}^\circ$ and $180{}^\circ$ is called an obtuse angle. Straight Angle An angle whose measure is $180{}^\circ \,\,\text{is}$called a straight angle.     Reflex Angle An angle whose measure is more than $180{}^\circ$ and less than $360{}^\circ$is called a reflex angle.   Complementary Angle Two angles whose sum is $90{}^\circ \,\,\text{is}$ called the complimentary angle. Complementary angle of any angle $\theta$ is$90{}^\circ -\theta$.   Supplementary Angle Two angles whose sum is $180{}^\circ \,\,\text{is}$ called supplementary angles. Supplementary angle of any angle $\theta$ is$180{}^\circ -\theta$.   Adjacent Angle Two angles are said to be adjacent if they have a common vertex and one common arm. In the following figure $\angle AOC$ and $\angle COB$are adjacent angles.     Vertically Opposite Angles Two angles are said to be vertically opposite angles if they are formed at the intersecting point of two lines.     In the figure given more...

#### Notes - Algebraic Expressions

Algebraic Expressions   In an algebraic expression constant and variables are linked with arithmetic operations. The value of unknown variable is obtained by simplification of the given expression.   Terms of an algebraic Expression   Variables Alphabetical symbols used in algebraic expressions are called variables a, b, c, d, m, n, x, y, z ........... etc. are some common letters which are used for variables.   Constant Terms The symbol which itself indicate a permanent value is called constant. All numbers are constant. $6,10,\frac{10}{11},15,-6,\sqrt{3}....$etc. are constants because, their values are fixed.   Variable Terms A term which contains various numerical values is called variable term. For example. Product of $\text{X=4 }\!\!\times\!\!\text{ }\,\text{X=4X}$Product of $\text{2,X,}{{\text{Y}}^{2\,}}$ and $\text{Z=}\,\text{2 }\!\!\times\!\!\text{ X }\!\!\times\!\!\text{ }{{\text{Y}}^{\text{2}}}\text{ }\!\!\times\!\!\text{ Z=2X}{{\text{Y}}^{\text{2}}}\text{Z}$ Thus, 4X and $\text{2X}{{\text{Y}}^{\text{2}}}\text{Z}$ are variable terms   Types of Terms There are two types of terms, like and unlike. Terms are classified by similarity of their variables.   Like and unlike Terms The terms having same variables are called like terms and the terms having different variables are called unlike terms. For example, $6x,\,x,\,-2x,\,\frac{4}{9}x,$are like terms and $6x,\,2{{y}^{2}},\,-9{{x}^{2}}yz,4xy,$are unlike terms.   Coefficient A number or a symbol multiplied with a variable in an algebraic expression is called its coefficient. In$-6{{m}^{2}}np$, coefficient of$n{{m}^{2}}p$ is $-6$ because ${{\text{m}}^{\text{2}}}np$is multiplied with $-6$ to from $-6{{m}^{2}}np$. The variable part of the term is called its variable or literal coefficient. In$-\frac{5}{4}abc$, variable coefficients are a, b and c. The constant part of the term is called constant coefficient. In term$-\frac{5}{4}abc$, constant coefficient is$-\frac{5}{4}$.   Example: Sign of resulting addition of two like terms depends on which one of the following? (a) Sign of biggest term (b) Sign of smallest term (c) Sign of positive term (d) Sign of negative term (e) None of these Answer (a)   Operations on Algebraic Expressions When constant and variables are linked with any of the following fundamental arithmetic operations i.e. addition, subtraction, multiplication and division, then the solution of the expression is obtained by simplification of the expression.   Addition and Subtraction of Terms The addition of two unlike terms is not possible and their addition is obtained in the same form. Addition of $2x+3x$ is $5x$ but the addition of $2x+3y$ is$2x+3y$. Subtraction of two like terms is same as the subtraction of whole numbers. For example,$4x-2x=2x$   Example: Simplify: $(2{{x}^{2}}+{{x}^{2}})-(5{{x}^{2}}+11{{x}^{2}})$ (a) $15{{x}^{3}}$                   (b) $15{{x}^{2}}$      (c) $-3{{x}^{2}}$                    (d) $13{{x}^{2}}$ (e) None of these   Answer (c) Explanation:$(2{{x}^{2}}+{{x}^{2}})-(5{{x}^{2}}+11{{x}^{2}})$ = $3{{x}^{2}}-16{{x}^{2}}=-13{{x}^{2}}$   Example: Evaluate: $[\{({{x}^{2}}+3{{x}^{2}})-({{x}^{2}}+{{x}^{2}})5\}\div x]$ (a) $-10x$                     (b) $-15x$ (c) $-6x$                                   (d) $10x$ (e) None of these Answer (c) Explanation:$(4{{x}^{2}}-5\times 2{{x}^{2}})\div x=$$\frac{4{{x}^{2}}-10{{x}^{2}}}{x}$ $=\frac{-6{{x}^{2}}}{x}=-6x$   Equation An equation is a condition on a variable. For example, the expression $10x+3=13$ is an equation which describe that the variable is equal to a fixed number. This value itself is called the solution of the equation. Thus,$10x+3=$$13\Rightarrow 10x$$=13-3=$$10\Rightarrow x=1$ Here the definite value of the variable x in the equation $10x+3=13$   Note: (i) An equation has two sides, LHS and RHS, between them more...

#### Notes - Ratio and Proportion

Ratio and Proportion   Ratio Ratio of two quantities is the comparison of the given quantities. Ratio is widely used for comparison of two quantities in such a way that one quantity is how much increased or decreased by the other quantity.   For example, Peter has 20 litres of milk but John has 5 litres, the comparison of the quantities is said to be, Peter has 15 litres more milk than John, but by division of both the quantity, it is said that Peter has, $\frac{20}{5}=4$ times of milk than John. It can be expressed in the ratio form as$4:1$   Note: In the ratio$a:b$$(b\ne 0)$, the quantities a and b are called the terms of the ratio and the first term (ie. a) is called antecedent and the second term (ie. b) is called consequent.   Simplest form of a Ratio If the common factor of antecedent and consequent in a ratio is 1 then it is called in its simplest form.   Comparison of Ratio Comparison of the given ratios are compared by first converting them into like fractions, for example to compare $5:6,\text{ }8:13\text{ }and\text{ }9:16$first convert them into the fractional form i.e. $\frac{5}{6},\frac{8}{13},\frac{9}{16}$. The LCM of denominators of the fractions$=2\times 3\times 13\times 8=624$ Now, make denominators of every fraction to 624 by multiplying with the same number to both numerator and denominator of each fraction. Hence,$\frac{5}{6}\times \frac{104}{104}=$$\frac{520}{624},\frac{8}{13}\times \frac{48}{48}$$=\frac{384}{624}$and$\frac{9}{16}\times \frac{39}{39}$$=\frac{351}{624}$.Equivalent fractions of the given fractions are $\frac{520}{624},\frac{384}{624},\frac{351}{624}$. We know that the greater fraction has greater numerator, therefore the ascending order of the fractions are, $\frac{351}{624}<\frac{384}{624}<\frac{520}{624}$ or $\frac{9}{16}<\frac{8}{13}<\frac{5}{6}$ or $9:16<8:13<5:6$, thus the smallest ratio among the given ratio is $9:16$and greatest ratio is$5:6$.   Equivalent Ratio The equivalent ratio of a given ratio is obtained by multiplying or dividing the antecedent and consequent of the ratio by the same number. The equivalent ratio of $\text{a}\,\,\text{:}\,\,\text{b}$ is $\text{a}\,\times \,\text{q}\,\,\text{:}\,\,\text{b}\,\times \,\text{q}$whereas, a, b, q are natural numbers and q is greater than 1.   Hence, the equivalent ratios of $5:8$are, $\frac{5}{8}\times \frac{2}{2}=\frac{10}{16}$ or$10:16$, $\frac{5}{8}\times \frac{3}{3}=\frac{15}{24}$ or$15:24$, $\frac{5}{8}\times \frac{12}{12}=\frac{60}{96}$ or$60:96$.   Example: Mapped distance between two points on a map is 9 cm. Find the ratio of actual as well as mapped distance if 1 cm = 100 m. (a) $10000:1$                (b) $375:1$         (c) $23:56$                    (d) $200:1$ (e) None of these Answer (a)   Explanation: Required ratio =$900\times 100:9=$ $90000:9=10000:1$   Example: Consumption of milk in a day is 6 litre. Find the ratio of Consumption of milk in month of April and quantity of milk in a day? (a) $99:2$                     (b) $30:1$         (c) $123:3$                    (d) $47:3$ (e) None of these Answer (b) Explanation: Required ratio $=30\times 6:6=30:1$   Proportion The equality of two ratios is called proportion. If a cake is distributed among eight boys and each boy gets equal part of the cake then cake is said to be distributed in proportion. The simplest form of ratio $12:96$is $1:8$and$19:152$is $1:8$therefore, $12:96$and $19:152$ are in proportion and written as $12:96::19:152$or more...

#### Notes - LCM and HCF

LCM and HCF   LCM (Least Common Multiple) LCM of two or more numbers is their least common multiple. LCM of 4 and 6 is 12, it means, 12 is the least common multiple of 4 and 6, therefore, 12 is exactly divisible by each of 4 and 6.   LCM by Prime Factorization Method The following steps are used to determine the LCM of two or more numbers by prime factorisation method: Step 1: Find the prime factors of each number. Step 2: Product of highest power of prime factors is their LCM.   LCM by Division Method The following steps are used to determine the LCM of two or more numbers by division method: Step 1: Numbers are arranged or separated in a row by commas. Step 2: Find the number which divides exactly atleast two of the given numbers. Step 3: Follow step 2 till there are no numbers (atleast two) divisible by any number. Step 4: LCM is the product of all divisors and indivisible numbers.   Example: Find the least number which is exactly divisible by each of 28 and 42. (a) 64                            (b) 84 (c) 52                            (d) All of these (e) None of these Answer (b)   Explanation: $28=2\times 2\times 7,\,\,42=2\times 3\times 7$            LCM =$2\times 2\times 3\times 7=84$   HCF (Highest Common Factor) Highest Common Factor is also called Greatest Common Measure (GCM) or Greatest Common Divisor (GCD). H.C.F of two or more numbers is the greatest number which exactly divides each of the numbers.   HCF by Prime Factorization Method The HCF of two or more numbers is obtained by the following steps: Step 1: Find the prime factors of each of the given number. Step 2: Find the common prime factors from prime factors of all the given numbers. Step 3: The product of the common prime factors is their HCF.   HCF by Continued Division Method The HCF of two or more numbers can also be obtained by continued division method. The greatest number is considered as dividend and smallest number as divisor.   Follow the following steps to perform the HCF of the given numbers: Step 1: Divide the greatest number by smallest. Step 2: If remainder is zero, then divisor is the HCF of the given number. Step 3: If remainder is not zero then, divide again by considering divisor as new dividend and remainder as new divisor till remainder becomes zero. Step 4: The HCF of the numbers is last divisor which gives zero remainder.   HCF of more than two Numbers The HCF of more than two numbers is the HCF of resulting HCF of two numbers with third number. Therefore, HCF of more than two numbers is obtained by finding the HCF of two numbers with third, fourth and so on.   HCF of Larger Numbers The HCF of smaller number (One or two digit numbers) is simply obtained by division but division of larger numbers take more time, more...

#### Notes - Fractions and Decimals

Fraction and Decimals   Fraction Fraction is a method for representing the parts of a whole number. An orange is divided into two equal parts and so the first part of orange is half of the whole orange and represented by $\frac{1}{2}$ of the orange.   Types of Fractions   Proper Fractions A fraction whose numerator is less than denominator is called a proper fraction. $\frac{3}{5}$? $\frac{1}{2}$? $\frac{7}{9}$ are Proper fractions.   Improper Fractions A fraction is called improper fraction even if: Ø  It has smaller denominator than numerator Ø  It has equal numerator and denominator $\frac{6}{5},\,\,\frac{5}{2},\,\,\frac{109}{34},\,\,\frac{6}{6}$   Simplest form of a Fraction A fraction is said to be in the simplest or lowest form if its numerator and denominator have no common factor except 1.   Mixed Fractions Combination of a proper fraction and a whole number is called mixed fraction. Every mixed fraction has a whole and a fractional part.   Like and Unlike Fractions When two or more fractions have same denominator then they are called like fractions whereas unlike fractions do not have equal denominators.   Equivalent Fractions Two fractions are said to be equivalent if they are equal to each other. Two equivalent fractions may have a different numerator and a different denominator.   Example: Convert $\frac{11}{2}$ into a mixed fraction.   (a) $5\frac{1}{2}$                                 (b) $3\frac{1}{2}$ (c) $\frac{1}{2}$                                   (d) All the above (e) None of these Answer (a)   Example: $\frac{5}{7},\,\frac{1}{2},\,\frac{2}{3}$are: (a) like fractions              (b)  unlike fractions (c) equivalent fractions     (d) Mixed fractions (e) None of these Answer (b)   Operations on Fractions   Addition of Like Fractions Addition of like fractions is the addition of their numerators and common denominator is the denominator of the resulting fraction.   Addition of numerators Hence, the sum of like fractions = $\frac{\text{Addition}\,\text{of}\,\text{numerators}}{\text{Common}\,\text{denominator}}$ Subtraction of Like Fractions Subtraction of like fractions is same as its addition except that addition is converted into subtraction. Let two like fractions are $\frac{567}{456}\text{and}\,\frac{4546}{456}$ Their subtraction=$\frac{\text{Subtraction}\,\text{of}\,\text{its}\,\text{numerators}}{\text{Common}\,\text{denominator}}$   Multiplication of Fractions The following are the steps to perform the multiplication of like fractions: Step 1: Multiply the numerators and multiply the denominators. Step 2: Write the answer in lowest form.   or, Product of fractions= $\frac{\text{Product}\,\text{of}\,\text{numerators}}{\text{Product}\,\text{of}\,\text{denominators}}$   Division of Fractions Division of fractions is multiplication of the dividend by reciprocal of the divisor.   Example: Evaluate: $\left\{ \left( \frac{3}{5}-\frac{7}{11}\times \frac{1}{2} \right) \right\}+\frac{9}{121}$ (a) $\frac{3}{121}$                               (b) $\frac{43}{121}$ (c) $\frac{431}{1210}$                          (d) All the above (e) None of these Answer (c)   Explanation:   $\left\{ \left( \frac{3}{5}-\frac{7}{11}\times \frac{1}{2} \right) \right\}+\frac{9}{121}=\frac{3}{5}-\frac{7}{22}+\frac{9}{121}$ $=\frac{726-385+90}{1210}$ $=\frac{431}{1210}$   Example: What should be divided by $\frac{\text{6}}{\text{11}\,}\,\text{to}\,\text{get}\,\frac{\text{3}}{\text{5}}$?   (a) $\frac{18}{55}$                  (b) $\frac{8}{55}$  (c) $\frac{55}{18}$                  (d) $\frac{30}{33}$  (e) None of these             Answer (a) Explanation: Required number =$\frac{6}{11}\times \frac{3}{5}=\frac{18}{55}$ Decimal Digits of decimal number are separated by a dot (.) called decimal point. Digits at the left from the dot (decimal) are called whole part and digits at the more...

#### Notes - Environment

Environment   Water Water is an abiotic component of the environment which is essential for the survival of life on the earth. It is present on the earth in all three states solid, liquid and gas. It covers about 71% of the earth surface.   Importance of Water It is the water which makes life possible on earth. Without water existence of life was not possible on the earth. Therefore, water is very important for all of us. v  Water is essential for the survival of life. v  Water provides shelter to the large variety of plants and animals. v  Plants use water for preparing food. v  Water is essential for germination of seeds and their growth.   Uses of Water Water is used for different purposes in our day to day life v  Water is used for drinking, bathing, cooking and cleaning clothes. v  Water is used for irrigation in agriculture. v  Water is used in the industries for the production of various substances. v  Water is used for the production of electricity.   States of Water Water is found on earth in all the three states.   Solid: Snow is the solid state of water. When water is cooled, it is converted into ice. This process is known as freezing or solidification.   Liquid: When ice is heated, it is converted into water. This process is known as melting. Condensation is the process by which water vapor cooled down to convert into water.   Gas: Water vapor is gaseous state of water. When liquid water is heated, it gets converted into water vapor. This process is known as evaporation.   Water Cycle The continuous circulation of water from the earth's surface to atmosphere and from the atmosphere back to the earth is called water cycle.     Due to sunlight water from the different sources converts into water vapor. These water vapors rise up in the atmosphere and condense to water drops forming cloud. Then they return back to the surface of earth in the form of rain.   Sources of Water Oceans, seas, lakes, rivers, ponds, rainwater and ground water are the sources of water.   Rain Water: Rainwater is the purest form of water. It collects on the earth in the form of surface water and underground water.   Surface Water: Water present on the surface of the earth in the form of oceans, seas, rivers, lakes, ponds and streams is called surface water. Ocean contains almost 97% of water present on the earth. But it is saline therefore it is unfit for drinking.   Underground Water: Some of the rainwater seeps through the soil and gathers more...

#### Notes - Electricity and Magnets

Electricity and Magnets   Electricity Electricity is a form of energy called electrical energy. We can convert electrical energy into various other forms of energies easily.   Electric Circuit The path through which electric current can flow is known as electric circuit. A simple electric circuit is made up of a bulb, wire and an electric cell. An electric cell has two terminals: a positive terminal and a negative terminal. A wire is connected from positive terminal to negative terminal of the cell and the bulb is connected to the wire so that current can flow through bulb.     Closed Circuit: When there is no gap in an electric circuit or the normal path of current has not been interrupted, the circuit is known as closed or complete circuit.   Open Circuit: When there is a gap in an electric circuit or the normal path of current has been interrupted, the circuit is known as an open circuit or incomplete circuit.   Conductors and Insulators The substances which allow electric current to pass through them are called conductors. For example, copper, gold, silver, aluminium, iron, etc. are good conductors of electricity. The substances which do not allow electric current to pass through them are called insulators. For example, wood, plastic, paper, rubber, etc are insulators.   Electric Cell An electric cell is a device which can generate electric current in a closed circuit. It is small and easily portable so it is very useful for us. There are a number of machines like watches, calculators, toys, cars, etc. in which electrical cell is used to produce electric current. Dry cell, button cell, solar cell are the examples of electric cell.   Dry Cell A dry cell is a cylindrical device in which a number of chemicals are stored. It has a metal cap on one side called positive terminal and a metal sheet at other side called negative terminal. It produces electric current from the chemical stored inside it.       Electric Bulb An electric bulb is a device which produces light energy using electrical energy. It consists of a glass bulb fixed on a metal case, a thin wire fixed between the two thick wires called filament of the bulb and the gas filled inside the glass bulb. When electric current passes through the filament, it emits light which makes the bulb glow.     Magnet Magnet is a substance which attracts magnetic materials such as iron, nickel, steel and cobalt. Magnets are of different shapes and sizes. For example, U-shaped magnet, cylindrical magnet, bar magnet, etc. Each magnet has two poles, south pole and north pole.   Magnetic Materials: The materials which are attracted by a magnet are called magnetic materials. For example, iron, nickel, steel and cobalt are magnetic materials. Magnetic materials can be converted into magnets by the process of more...

#### Notes - Light, Shadow and Reflection

Light, Shadow and Reflection   Light Light is a form of energy visible to the human eye that is radiated by moving charged particles. Speed of light in air is about$3\times {{10}^{8}}m\text{/}s$.   Ray: It is a very narrow and straight path of light.   Beam: It is broader and consists of several rays.   Sources of Light The objects which give out light are called sources of light. Sun, star, bulb, torch, candle, lantern, lamp, etc. are the sources of light.   Luminous and Non-luminous Objects The objects which produce their own light are called luminous objects. Sun, stars, bulb, torch, candle, lantern, lamp etc. are luminous objects. The objects which do not produce light on their own are called non-luminous objects. Table, fan, book, chair, etc. are non-luminous objects.   Transparent, Translucent and Opaque Objects Transparent Objects: The objects which allow light to pass through them. For example glass, water, air, etc.   Translucent Objects: The objects which allow light to pass through them partially. For example, oiled paper, tissue paper, muddy water, ground glass, etc.   Opaque Objects: The objects which do not allow light to pass through them. For example, wall, blackboard, metal sheet, etc.   Shadow If an object is placed in front of a source of light, the object cast its shade which is known as shadow. All the opaque objects produce their shadow on the opposite side to the source of light. The shape of shadow depends on the followings: v  Shape of the object v  Size of the source of light v  Position of the source of light   Reflection of Light When a ray of light falls on the surface of a mirror, they are sent back. This phenomenon is known as reflection of light.     (r=angle of reflection) = (i=angle of incidence) The ray which falls on the surface of a mirror is called an incident ray. The ray which is sent back after reflection is called reflected ray.   Spherical Mirrors A spherical mirror is a mirror which has the shape of a piece cut out of a spherical surface. There are two types of spherical mirrors: concave and convex.     Reflecting surface of a concave mirror bulges inward whereas reflecting surface of a convex mirror bulges outward.   Images Real Image The images which are inverted and can be taken on the screen are called real images   Virtual Image The images which are erect and cannot be taken on the screen are called virtual images.

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