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.

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...

Day | Number of cakes | = 10 cakes |

Monday | ||

Tuesday | ||

Wednesday | ||

Thursday | ||

Friday |

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...

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...

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...

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...

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...

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...

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...

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...

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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