THE FIRST EMPIRE
We
have read about how small states, or janapadas, came to be formed in different
parts of the subcontinent and eventually conquered neighbouring states to form
larger states, or mahajanapadas. As more territories were conquered, the
mahajanapadas gave way to empires. The empires favoured dynastic rule, i.e.,
rulers from the same family succeeded each other to the throne.
Earth
has two types of motions:
Rotation - Rotation can be defined as the movement of the Earth on its axis.
Revolution-
Revolution can be defined as the movement of the Earth on its orbit around the
Sun
This
rotation and revolution are responsible for causing day and night, and
change in seasons and climate on the Earth.
ROTATION
We
know that the Earth spins on its axis, an imaginary line running north to south
across its center. The Earth rotates from west to east and completes one
rotation in 24 hours. This rotation leads to day and night on the planet. We
all know that the Sun rises in the east and sets in the west. It appears to
move from east to west in the sky. But in reality, the Sun is stationary and it
is the Earth which is rotating from west to east. For example, when we travel
in a car, things outside the car like buildings, trees, etc., appear to be
moving backwards. But we know that they are actually stationary and it is we
who are moving forward in the car.
When
the Earth rotates on its axis, only one half of its surface faces the Sun at a
time. This half of the Earth receives the Sun's light and heat and experiences
day time. The part of the Earth that faces away from the Sun experiences
darkness and night time. The circle of illumination is an imaginary line that
divides the half of the Earth that experiences day from that which experiences
night.
As
the Earth rotates, different regions experience the phenomena of day and night.
Look
at the image given below.
Consider
a point on the Earth's surface, say X. We know that the Earth rotates from west
to east. This means, the point X will at some time move east to position R. At
this position, it receives diffused light from the Sun. This time of the day
when the Sun is not visible and yet there is some light is called dawn.
In
time X will reach position P and experience sunrise. This denotes the time when
the Sun appears on the eastern horizon. When X reaches N, it will directly face
the Sun. This time of the day when sunlight falls directly on X is called noon
or mid-day.
After N, X will begin to move away from the Sun. At E, the Sun will appear to go down on the western horizon. This is the time of sunset. At G, X will receive some diffused light for a while after which it will experience darkness. This time of the day is called dusk or twilight. At H, X will be in complete darkness. This time is called midnight. As the Earth spins on its axis, these positions will keep repeating every 24 hours.
If
the Earth did not rotate it would always be day in the part of the Earth facing
the Sun. This part would experience continuous warmth. It would always be night
in the half facing away from the Sun. This half would remain freezing cold all
the time. Life would not have been possible in such extreme conditions.
REVOLUTION
The
Earth revolves around the Sun on a fixed path or orbit. This orbit is not circular,
but elliptical in shape. The rotation as well as the revolution of the Earth
takes place in the same direction. The Earth completes one revolution around
the Sun in 365 days and 6 hours. Therefore, revolution is also called annual
motion of the Earth. This motion causes change of seasons on the Earth. As the
Earth's orbit is elliptical, the Earth is closer to the Sun at certain points
on the orbit and far from the Sun at certain points. The Earth is said to be in
perihelion when its distance from the Sun is minimum. When the distance between
the Earth and the Sun is maximum, it is said to be in aphelion.
Perihelion and aphelion
Think
and Answer
Does
the Earth experience any other motion apart from rotation and revolution? It is
believed that every point in the entire universe is in motion relative to every
other point, because the entire universe is rapidly expanding. Besides the Earth's
movement around the Sun, the Earth along with the entire Solar System is moving around the center of the
Milky Way Galaxy. It takes our Solar System 225 million years to make one trip around the galaxy.
LEAP YEAR
The
Earth completes one revolution in 365 days and 6 hours. For our convenience, we
consider one year to have 365 days and ignore 6 hours. Every 4th years, the 6
hours add up to become 24 hours i.e., one day. The extra day is added to the
month of February. Therefore, every four years, February has 29 days instead of
28 days. So every fourth year has 366 days. Such a year is known as a leap
year.
A
leap year is always a multiple of 4. The Romans first designated February 29 as
leap day. A person born on February 29 is called a "leapling" or a
'leaper".
INCLINATION OF THE EARTH'S AXIS
While
it revolves around the Sun, the Earth remains tilted to one side. We study the
tilt of the Earth through its axis. The axis is an imaginary line passing
through the centre of the Earth around which the Earth rotates.
The
axis makes an angle of 66½° with the orbital plane of the Earth. The orbital
plane can be defined as the plane formed by the Earth's orbit. The axis makes
an angle of 23/½° with the plane perpendicular to the orbital plane. The two
ends of the axis are called the North Pole and the South Pole.
EFFECTS OF TILTED AXIS AND REVOLUTION
(a) Unequal length of days and nights
Days
are longer in places nearer to the North Pole than the South Pole. At the
Equator, the length of the illuminated and dark parts of the circle is equal. That
means any point on the Equator has almost equal length of day and night all
through the year. As we go north, the length of the illuminated part of the
parallel is more than the darkened part. It means that days become longer and
nights become shorter when we move from the Equator towards the North Pole.
In
fact, the North Pole experiences six months of daylight. When the South Pole is
tilted towards the Sun, the Southern Hemisphere receives more heat in
comparison to the Northern Hemisphere. Therefore, the Southern Hemisphere
experiences summer, while the Northern Hemisphere experiences winter. As seen
in the figure, the Northern Hemisphere has longer nights and shorter days.
Places near the North Pole have six months of darkness.
(b) Change in temperature
Summers are hot and winters are cold. This is because the hemisphere facing the Sun receives more direct rays of the Sun, while the hemisphere facing away receives more slanting rays of the Sun. Direct rays have more heating capacity than slanting rays. This is because vertical rays get concentrated on a smaller area whereas slanting rays get spread over a wider area. A change in temperature affects the weather conditions of a place. A change in weather conditions leads to a change of seasons.
Think and Answer Why is the Equator hot and wet
throughout the year? The Earth bulges at the Equator, so this part is always
close to the Sun and therefore, extremely hot. Warm air can hold more water
than cold air. Warm air is also less dense than cold air. As warm air rises,
it cools and the water vapour condenses and falls as rain. At the Equator,
there is an overall upward movement of air. This causes more condensation and
hence more rain. Think and Answer What is the average length of day and
night at the Equator? At the Equator, every day and every
night is 12 hours long. |
(c) Changing seasons
The
term 'season' refers to a period of the year when general weather conditions
remain the same. As the season changes, the weather conditions also change
consecutively. The four major seasons experienced in most parts of the world
are summer, autumn, winter, and spring. The interval between the seasons is
about three months.
CHANGE IN SEASONS
The
change in the position of the Earth as it moves around the Sun bring and the
tilt in it's axis about a change in seasons. This phenomenon is best understood
by studying the four positions of the Earth during its revolution around the
Sun.
The position on June 21
On
this date, the North Pole is tilted towards the Sun. The rays of the Sun fall
vertically on the Tropic of Cancer (23/½°N). It is summer season in the Northern
Hemisphere and winter season in the Southern Hemisphere. The position of the Earth on June
21 is also called 'summer solstice' in the Northern Hemisphere, and the 'winter
solstice' in the Southern Hemisphere.
The
term solstice refers to that time when the Sun is directly overhead one of the tropics. Because a large
portion of the Northern Hemisphere receives sunlight, regions lying north of
the equator experience the longest day and the shortest night on June 21. The
nights are longer than the days in areas in the Southern Hemisphere on this
day.
The position on December 22
On
this date, the South Pole is tilted towards the Sun and the rays of the Sun
fall vertically on the Tropic of Capricorn (23/½°S). It is winter season in the
Northern Hemisphere and summer season in the Southern Hemisphere. The position
of the Earth on December 22 is called 'winter solstice' in the Northern
Hemisphere, which experiences the shortest day of the year. It is called
'summer solstice for the Southern Hemisphere, which experiences longer days and
shorter nights.
The positions on March 21 and September 23
On
these two dates, neither of the Poles is inclined towards the Sun. The rays of
the Sun fall vertically over the Equator. As a result, on these days, days and
nights are of equal duration throughout the world. This is called an equinox.
The weather conditions in both the hemispheres are almost similar. It is
neither hot nor cold in either hemisphere.
There
is spring season in one hemisphere and autumn in the other. March 21 is called
'spring equinox' in the Northern Hemisphere and 'autumn equinox' in the
Southern Hemisphere. September 23 is called 'autumn equinox' in the Northern
Hemisphere and 'spring equinox' in the Southern Hemisphere.
Revision
Rotation: Movement of the Earth on its axis.
Axis: An
imaginary line running north to south across the centre of the Earth.
Circle of illumination: An imaginary circle that divides the half
of the Earth that experiences day from that which experiences night.
Dawn:
Time of the day when the Sun is not visible and yet there is some light.
Sunrise: The
time when the Sun appears on the eastern horizon.
Noon: Also
known as mid-day; time of the day when the sun is directly overhead a place.
Sunset:
The time when the Sun appears to go down on the western horizon.
Dusk:
Also known as twilight; time of the day when a place gets some diffused light
from the Sun before it gets completely dark.
Rotation causes
day and night. Revolution and earth's titled axis causes unequal lengths of day
and night, change of seasons, and changes in temperatures.
Revolution: Movement of the Earth on its orbit around the Sun.
Perihelion: When the distance between the Earth and the Sun is
minimum.
Aphelion: When
the distance between the Earth and the Sun is maximum.
Orbital plane: An imaginary plane formed by the Earth's orbit.
Season:
Refers to a period of the year when general weather conditions remain the same.
Solstice:
Refers to that time when the Sun is directly overhead one of the tropics.
Equinox: Refers
to the time when days and nights are of equal duration throughout the world.
Regions
lying in the Northern Hemisphere experience the longest day on June 21 and the
shortest day on December 22.
On
March 21 and September 23, days and nights are of equal duration throughout the
world.
1. What is the
cause of day and night on Earth?
a) The Earth's
revolution around the Sun
b) The Earth's rotation on its axis
c) The Sun moving from east to west
d) The Earth’s tilt
Answer: b)
The Earth's rotation on its axis
2. In which
direction does the Earth rotate on its axis?
a) East to west
b) West to east
c) North to south
d) South to north
Answer: b)
West to east
3. How long does
it take for the Earth to complete one full rotation?
a) 12 hours
b) 24 hours
c) 365 days
d) 48 hours
Answer: b)
24 hours
4. What imaginary
line divides the part of the Earth experiencing day from the part experiencing
night?
a) Axis of
rotation
b) Equator
c) Circle of illumination
d) Tropic of Cancer
Answer: c)
Circle of illumination
5. Why does the
Sun appear to move from east to west in the sky?
a) The Sun is
moving around the Earth
b) The Earth rotates from east to west
c) The Earth rotates from west to east
d) The Earth is stationary
Answer: c)
The Earth rotates from west to east
6. When it is
daytime on one half of the Earth, what is happening on the other half?
a) It is also day
b) It is night
c) It is sunset
d) It is dawn
Answer: b)
It is night
7. Which of the
following best describes the axis of the Earth?
a) A real line
from the North to the South Pole
b) An imaginary line from the North to the South Pole
c) A real line from east to west
d) An imaginary line running around the Equator
Answer: b)
An imaginary line from the North to the South Pole
8. In which
dynasty was Aryabhatta born?
a) Maurya Dynasty
b) Gupta Dynasty
c) Chola Dynasty
d) Mughal Dynasty
Answer: b)
Gupta Dynasty
9. What
significant discovery did Aryabhatta make about Earth's motion?
a) The Earth
revolves around the Sun
b) The Earth rotates about its axis daily
c) The stars move across the sky
d) The Sun revolves around the Earth
Answer: b)
The Earth rotates about its axis daily
10. Aryabhatta was
known for his contributions to which fields?
a) Medicine and
Biology
b) Architecture and Art
c) Mathematics, Astronomy, and Physics
d) Music and Literature
Answer: c)
Mathematics, Astronomy, and Physics
11. What was the
prevailing belief before Aryabhatta’s theory about Earth's rotation?
a) The Earth was
stationary, and the sky rotated
b) The Earth rotated around the Sun
c) The stars and planets did not move
d) The Sun rotated around the Earth
Answer: a)
The Earth was stationary, and the sky rotated
12. What would
happen if the Earth did not rotate?
a) There would be
no change in seasons
b) Half of the Earth would experience continuous day and warmth
c) Both halves of the Earth would experience continuous day
d) The Earth would remain at the same temperature throughout
Answer: b)
Half of the Earth would experience continuous day and warmth
13. What is the
shape of Earth's orbit around the Sun?
a) Circular
b) Elliptical
c) Square
d) Irregular
Answer: b)
Elliptical
14. How long does
it take for the Earth to complete one revolution around the Sun?
a) 24 hours
b) 365 days
c) 365 days and 6 hours
d) 366 days
Answer: c)
365 days and 6 hours
15. What is the
annual motion of the Earth?
a) The Earth’s
rotation on its axis
b) The Earth's revolution around the Sun
c) The movement of the Sun around the Earth
d) The revolution of the Moon around the Earth
Answer: b)
The Earth's revolution around the Sun
16. When the Earth
is closest to the Sun, what is this position called?
a) Aphelion
b) Perihelion
c) Solstice
d) Equinox
Answer: b)
Perihelion
17. When the Earth
is farthest from the Sun, it is said to be in which position?
a) Perihelion
b) Aphelion
c) Solstice
d) Equinox
Answer: b)
Aphelion
18. How long does
it take the Solar System to complete one trip around the Milky Way Galaxy?
a) 225 million
years
b) 1 million years
c) 365 days
d) 25,000 years
Answer: a)
225 million years
19. What causes
the change of seasons on Earth?
a) The Earth’s
rotation
b) The Earth’s revolution around the Sun
c) The Earth's distance from the Moon
d) The Earth's movement around the Milky Way
Answer: b)
The Earth’s revolution around the Sun
20. Why is an
extra day added to February every four years?
a) To make up for
6 hours added annually
b) To correct the Earth's orbit
c) To balance the months
d) To adjust for the leap year
Answer: a)
To make up for 6 hours added annually
21. What is a person
born on February 29 called?
a) Leaper
b) Leapling
c) Extra-born
d) Februaryite
Answer: b)
Leapling
22.At what angle
is the Earth's axis tilted with respect to the orbital plane?
a) 45°
b) 90°
c) 66½°
d) 23½°
Answer: c)
66½°
23. What is the
angle between the Earth's axis and a perpendicular to the orbital plane?
a) 23½°
b) 45°
c) 66½°
d) 90°
Answer: a)
23½°
24. What causes
the unequal length of days and nights on Earth?
a) The Earth's
elliptical orbit
b) The Earth's rotation
c) The tilt of the Earth's axis
d) The Earth’s proximity to the Sun
Answer: c)
The tilt of the Earth's axis
25.When the North
Pole is tilted towards the Sun, which hemisphere experiences summer?
a) Southern
Hemisphere
b) Northern Hemisphere
c) Equator
d) Both Hemispheres
Answer: b)
Northern Hemisphere
26. At the
Equator, how do the lengths of day and night compare throughout the year?
a) Day is always
longer
b) Night is always longer
c) Day and night are almost equal in length
d) Day is twice as long as night
Answer: c)
Day and night are almost equal in length
27. As you move
from the Equator towards the North Pole during summer, what happens to the
length of days?
a) Days become
shorter
b) Days become longer
c) Days remain the same length
d) Days and nights become equal
Answer: b)
Days become longer
28. Why are
summers hot and winters cold?
a) Because the
Earth’s orbit changes
b) Due to the angle of the Sun’s rays
c) The Sun emits more heat in summer
d) The Earth’s rotation speeds up in winter
Answer: b)
Due to the angle of the Sun’s rays
29. What happens
to the temperature when a hemisphere receives slanting rays of the Sun?
a) Temperature
increases
b) Temperature remains constant
c) Temperature decreases
d) Temperature fluctuates
Answer: c)
Temperature decreases
30. Why is the
Equator hot throughout the year?
a) The Equator is
always close to the Sun
b) The Sun emits more heat at the Equator
c) The Equator receives slanting rays of the Sun
d) The Equator moves towards the Sun during summer
Answer: a)
The Equator is always close to the Sun
31. Why does the
Equator experience more rain?
a) Warm air holds
less water than cold air
b) Warm air rises and cools, leading to condensation
c) The Sun heats up the air quickly
d) Cold air from the poles moves to the Equator
Answer: b)
Warm air rises and cools, leading to condensation
32. What is the
average length of day and night at the Equator?
a) 10 hours of day
and 14 hours of night
b) 12 hours of day and 12 hours of night
c) 14 hours of day and 10 hours of night
d) 16 hours of day and 8 hours of night
Answer: b)
12 hours of day and 12 hours of night
33. Why do places
near the North Pole experience six months of darkness?
a) The North Pole
is tilted away from the Sun for six months
b) The Sun does not shine on the North Pole
c) The Earth’s rotation stops during this time
d) The Sun moves to the Southern Hemisphere for six months
Answer: a)
The North Pole is tilted away from the Sun for six months
34. What is the
term 'season' used to describe?
a) A specific
month of the year
b) A period of the year with consistent weather conditions
c) The time when the Earth rotates on its axis
d) The day and night cycle
Answer: b)
A period of the year with consistent weather conditions
35. What causes
the change in seasons on Earth?
a) The Sun’s
distance from Earth
b) The tilt of Earth’s axis and its revolution around the Sun
c) The Earth's rotation
d) The movement of the Moon around the Earth
Answer: b)
The tilt of Earth’s axis and its revolution around the Sun
36. What is the
position of the Earth on June 21 called in the Northern Hemisphere?
a) Winter solstice
b) Spring equinox
c) Summer solstice
d) Autumn equinox
Answer: c)
Summer solstice
37. What happens
in the Northern Hemisphere on June 21?
a) The shortest
day of the year
b) Equal duration of day and night
c) The longest day and the shortest night of the year
d) Winter season
Answer: c)
The longest day and the shortest night of the year
38. On which date
does the Northern Hemisphere experience the winter solstice?
a) March 21
b) June 21
c) December 22
d) September 23
Answer: c)
December 22
39.What is the
position of the Earth on March 21 and September 23 known as?
a) Solstice
b) Equinox
c) Tilt day
d) Leap day
Answer: b)
Equinox
40. What happens
to the duration of day and night on March 21 and September 23?
a) Days are
shorter than nights
b) Days are longer than nights
c) Days and nights are of equal duration
d) Nights are longer than days
Answer: c)
Days and nights are of equal duration
41. What is March
21 called in the Northern Hemisphere?
a) Autumn equinox
b) Winter solstice
c) Summer solstice
d) Spring equinox
Answer: d)
Spring equinox
42. On December
22, where do the Sun's rays fall vertically?
a) Tropic of
Cancer
b) Tropic of Capricorn
c) Equator
d) North Pole
Answer: b)
Tropic of Capricorn
43. What season
does the Southern Hemisphere experience during the December 22 solstice?
a) Winter
b) Autumn
c) Summer
d) Spring
Answer: c)
Summer
44. What is
"Perihelion"?
a) When the Earth
is closest to the Sun
b) When the Earth is farthest from the Sun
c) The point where the Earth rotates fastest
d) When the Sun is directly overhead the Equator
Answer: a)
When the Earth is closest to the Sun
45. What is the
"Orbital plane"?
a) The path the
Earth takes while revolving around the Sun
b) The imaginary line passing through the Earth's center
c) The axis of the Earth
d) The imaginary plane formed by the Earth's orbit
Answer: d)
The imaginary plane formed by the Earth's orbit
46. What is meant
by "Season"?
a) A period of one
month with fluctuating weather
b) The time when Earth moves closest to the Sun
c) A period of the year when general weather conditions remain the same
d) A point in Earth’s orbit where days are longer than nights
Answer: c)
A period of the year when general weather conditions remain the same
47. What does
"Solstice" refer to?
a) The time when
days and nights are of equal duration
b) The time when the Sun is directly overhead one of the tropics
c) When the Earth is at its farthest point from the Sun
d) When the Earth’s rotation slows down
Answer: b)
The time when the Sun is directly overhead one of the tropics
48. What is an
"Equinox"?
a) When the Earth
is tilted towards the Sun
b) When the distance between Earth and Sun is equal
c) When days and nights are of equal duration throughout the world
d) The shortest day of the year in the Northern Hemisphere
Answer: c)
When days and nights are of equal duration throughout the world
49. When does the
Northern Hemisphere experience its longest day?
a) December 22
b) March 21
c) June 21
d) September 23
Answer: c)
June 21
50. When do days
and nights have equal duration worldwide?
a) June 21 and
December 22
b) March 21 and September 23
c) July 1 and January 1
d) April 15 and October 15
Answer: b)
March 21 and September 23
51. When does the
Northern Hemisphere experience its shortest day?
a) June 21
b) September 23
c) December 22
d) March 21
Answer: c)
December 22
The
objects which we see around us are made of different materials like wood,
glass, rubber, plastic, cotton, etc. They are of different shapes, sizes,
colours and uses. For example, table, chair, bag, books, clothes, birds, cars,
trees are all made of different materials. How do we group such a variety of
objects?
We
group objects on the basis of certain similarities and differences in their
properties. This type of grouping in which similar objects are placed together
is known as classification. Therefore, the above mentioned objects may be
classified as living or non-living. We can also classify them as naturally
occurring or man-made objects.
But why is it necessary to classify objects into groups?
OBJECTS
AROUND US
All
the objects that we see and feel around us have definite mass and occupy space.
We can say that these objects are made up of matter. Therefore, matter is defined as anything that has mass and occupies
space. The various objects and materials we discussed before, are all
matter. Air is also matter since it has mass and occupies space, though we
cannot see it. The amount of matter contained in an object is measured by its
mass. The space occupied by an object is known as its volume.
Matter
is made up of tiny particles called molecules. The
arrangement of molecules decides whether an object is a solid, liquid or a gas.
Solid: The molecules are tightly packed and a strong attractive force acts between them. So, they have a definite shape and volume.
Liquid:
The molecules in a liquid are loosely packed and the intermolecular attractive forces between them are weak. So, liquids do not have a definite shape but they have a definite volume and take the shape of the container in which they are kept.
Gas: The molecules in a gas are far apart from each other and there is hardly any attractive force acting between them. So, a gas does not have a fixed shape or volume. The molecules move around freely and occupy the entire space available to them.
Materials-All objects are made up of substances called materials.PROPERTIES OF MATERIALS
The
characteristics of materials, that enable us to separate one object from the
other, are called its properties. The properties of materials decide how and
for what purpose they can be used. For example, wood or steel would be the most
suitable material for making a cupboard but not clothes. Some of the properties
of materials are discussed below.
Appearance
It is the external property of matter that distinguishes one material from the other. How things appear to the eyes is called appearance.
Metals like iron, copper, aluminium, gold, etc., have a shining surface. This characteristic of metals is known as lustre. Materials like wood, plastic, paper or rubber do not possess lustre and appear dull. This characteristic of non-metals is termed as non-lustre.When metals are exposed to air, most of them lose their lustre and get tarnished due to the action of air and moisture.
On polishing or rubbing the surface with sandpaper, they regain their lustre once again. Therefore, we notice the lustre, only on their freshly cut surface. Gold and silver metals are made into ornaments due to their colour and lustre. Gold does not lose its shine on exposure to air, so ornaments made of this metal remain sparkling throughout.
Hardness
Metals
like lead, aluminium, copper and materials like wood, stone, etc., are hard.
Chalk, cotton, wax, etc., are soft materials. The shape of hard objects cannot
be changed by applying any amount of force but the shape of soft objects can be
altered easily. The property of hardness of a material decides the purpose for
which it can be used. For example, the materials used for making vehicles,
houses, roads, etc., should be hard while clothes should be made of soft
materials. The soft materials can also be scratched with our nails, but not the
hard materials. We can easily scratch a candle, made of wax, but it is not
possible to scratch a stone.
Materials
can also be smooth or rough to touch. The surface of steel utensils, polished
wood, etc., are smooth. Bricks, rocks and soil have rough surfaces. Therefore,
the materials can also be classified according to their smoothness or
roughness.
Lustre,
hardness, roughness or smoothness are some of the properties which describe the
appearance of a material. In addition to this, we can also describe the
appearance of a material by its size and weight i.e., whether it is large or
small or whether it is heavy or light.
Solubility
Materials
or substances like sugar or salt, when mixed with water, disappear completely
in it. We say that, sugar or salt has dissolved in water. Substances which
dissolve in water are known as soluble substances. Sand and chalk powder do not
dissolve in water. They are said to be insoluble substances.
Water is the most commonly used solvent since it readily dissolves a number of substances in it. Therefore, it is called a universal solvent. Being a universal solvent, water plays an important role in the functioning of our body.
Some liquids like glycerine, vinegar and lemon juice dissolve in water to form solutions. They are known as miscible liquids. Vinegar and lemon juice or vinegar and glycerine are miscible with each other. In both the cases, the solvent used is not water.
Cooking oil, kerosene oil, petrol, etc., do not
dissolve in water. They separate into two distinct layers when kept undisturbed
for some time. The liquids which do not mix with each other are known as
immiscible liquids. Sand is insoluble in water other are known as immiscible
liquids.
Gases like oxygen and carbon dioxide dissolve in water. These gases help the aquatic plants and animals to carry out the process of photosynthesis and respiration. Aerated or fizzy drinks also contain carbon dioxide dissolved in water under pressure.
Floatation
Certain
materials float on water whereas, others sink. This property is called
floatation. Generally, wood, leaves, plastic, paper and feathers float on water
whereas rocks glass, honey, sand and metals sink. We can test these materials
to see whether they float o sink in oil.
The materials which sink in water, will sink in oil, since oil is lighter than water. The materials which float in water, may float or sink in the oil, depending on the density of oil and the density of the materials. Hence, floating and sinking of objects will depend upon density of the liquid and the density of the objects.
Density
is a property of matter that describes how heavy an object is for its size.
Density compares the weight of a material to its volume. In some matter, the
molecules are more closely packed together. These materials have a higher
density. Scientists compare everything to water; which has density equal to 1
g/cm³. When the density of a material is less than one, it will float in water.
Materials with a density greater than one will sink in water.
The
shape of an object also affects the amount of liquid it displaces. Certain
heavy objects are able to float because of their shape. For example, the shape
of a ship allows it to float on water, despite the fact that it is very heavy.
Transparency:
The
amount of light that passes through an object depends on the material with
which it is made. Based on this property, materials are classified as transparent, translucent and opaque.
Transparent Materials: These materials allow light to pass through them easily. Air, glass, clear water and some plastics are transparent materials. We can see the objects clearly through these materials.
Translucent Materials:These materials allow light to pass
through them partially. Ground glass, oiled or waxed paper are translucent
materials. We cannot see the objects clearly through these materials. When you
cover the palm of your hands with a torch, you can see a dull red glow. Here,
the palm acts as a translucent object.
Opaque Materials: These materials do not allow light to pass through them at all. Metals, rocks, wood and cardboard are opaque materials. The objects are not visible through opaque materials.
So,
all the materials can be grouped in these three categories without any
confusion.
Thermal and Electrical Conductivity
Metals
like silver, copper, iron and aluminium become hot when they are heated over a
flame. Thus, they conduct heat. These materials are said to be good conductors
of heat.
Materials
like plastic, rubber, wood, etc., do not allow heat to pass through them. These
materials are called poor conductors or bad conductors of heat. The conduction
of heat through a substance is called its thermal
conductivity.
Both
pure water and air are bad conductors of heat. Pure water is bad conductor of
electricity. Impurities like acids and bases present in it make it a conductor
of electricity.
You
must have noticed that some cooking vessels like pressure cookers and frying
pans are made of metals but their handles are made of a plastic like material,
bakelite. This is because, metals being good conductors of heat warm up the
food quickly. Bakelite, being a bad conductor Lear of heat, does not get
heated. Therefore, the handles can be held easily while cooking food in them.
Materials which do not conduct electricity are known as bad
conductors or insulators.
Magnetic property
Certain substances have the property of being attracted by a magnet. Such materials are called magnetic materials. Metals like iron, cobalt and nickel are magnetic materials. Objects made of these metals will get attracted to the magnet. The ends of a magnet are called the north pole and south pole.
The
materials that are not attracted by a magnet are called non- magnetic
materials. Aluminium, copper, brass, wood, plastic, paper and rubber are some
of the non-magnetic materials.
Thus,
materials can be arranged into groups according to any of the above discussed properties. This type of
grouping makes it easier to find things when they are required. It also
facilitates the study of their properties and also observe any patterns in
these properties.
IMPORTANT TERMS
Materials: The substances
with which objects are made.
Classification: The process of
grouping things based on similarities and differences.
Matter: Matter is
anything that has mass and occupies space.
Appearance: How things appear
to the eyes.
Lustre: The shiny
appearance of materials.
Transparent
materials:
The materials which allow light to pass through them
Translucent
materials
: The materials which allow light to pass through them partially
Opaque
materials :
These materials do not allow light to pass through them at all)
Placing
similar things together is called grouping.
Grouping
makes it easier to find things when they are required.
Things
are grouped together for convenience and to study their properties.
Objects
are classified based on similarities and differences. Some materials are shiny
in appearance while others are not. Some are hard and some soft. Similarly,
some materials are rough, others are smooth.
Substances
which dissolve in water are called soluble substances while substances which do
not dissolve are called insoluble. Some materials float on water whereas some
sink in it.
1. What is the process of grouping objects with
similar properties called?
Identification
Classification
Separation
Observation
Answer: (b) Classification
Explanation: Classification is the
process of grouping objects based on their similarities and differences in
properties. It helps in organizing a wide variety of objects, making them
easier to study.
Q2. Which of the following can be used as a criterion
to classify objects?
Size and Color
Similarities and Differences
Price and Value
Age and Weight
Answer: (b) Similarities and Differences
Explanation: Objects are classified
based on similarities and differences in their properties such as material,
shape, size, or function. This helps us place similar objects together and
understand their relationships.
3. Why is it necessary to classify objects into
groups?
To create confusion
To make the study of objects easier and systematic
To eliminate some objects
To separate them into equal parts
Answer: (b) To make the study of objects
easier and systematic
Explanation: Classification helps in the
systematic study of objects by grouping similar items together, making it
convenient to understand and compare their characteristics.
4. How can objects be classified besides being living
or non-living?
According to their uses
As naturally occurring or man-made
Based on their weight
Based on their color
Answer: (b) As naturally occurring or
man-made
Explanation: Another common method of
classification is grouping objects into naturally occurring (e.g.,
trees, animals) and man-made (e.g., plastic, cars) objects, making it
easier to understand their origin and purpose.
5. Which of the following is a correct statement about
matter?
Matter has no mass or volume
Matter occupies space and has mass
Matter only exists in liquid form
Matter is always visible to the human eye
Answer: (b) Matter occupies space and
has mass
Explanation: Matter is defined as
anything that has mass and occupies space. This includes solids, liquids,
gases, and even air, which, though invisible, is still considered matter.
6. Which of the following is true about solids?
They have a definite shape but no definite volume
They have neither definite shape nor volume
They have a definite shape and volume
They do not occupy space
Answer: (c) They have a definite shape
and volume
Explanation: In solids, the molecules are tightly
packed, resulting in a definite shape and volume. The strong intermolecular
forces keep the structure intact.
7. What property of liquids differentiates them from
solids?
Liquids have a definite shape
Liquids do not have a definite shape but have a
definite volume
Liquids do not have volume
Liquids are made of tightly packed molecules
Answer: (b) Liquids do not have a
definite shape but have a definite volume
Explanation: Liquids have molecules that
are loosely packed, allowing them to take the shape of their container.
However, they still retain a definite volume.
8. Why do gases occupy the entire space available to
them?
Because their molecules are tightly packed
Because there is a strong force between the molecules
Because their molecules are far apart and move freely
Because gases have a definite shape and volume
Answer: (c) Because their molecules are
far apart and move freely
Explanation: In gases, the molecules are far apart,
and there is little to no attractive force between them. This allows them to
move freely and fill any container they are placed in, occupying all available
space.
9. Which of the following objects is made of more than
one material?
A wooden chair
A steel bridge
An aerated drink
A plastic bottle
Answer: (c) An aerated drink
Explanation: An aerated drink is
composed of water, sugar, and dissolved gas, making it an example of an object
made from multiple materials. Other examples like a wooden chair or steel
bridge are made from a single material.
10. What is the term used for the external property of
matter that distinguishes one material from another?
Solubility
Hardness
Appearance
Miscibility
Answer: (c) Appearance
Explanation: Appearance refers to how
materials look or appear to the eyes. It is an external property that helps
distinguish one material from another, such as the shiny surface of metals
versus the dull appearance of non-metals.
11. Which of the following materials is known for
retaining its lustre even after exposure to air?
Iron
Gold
Copper
Aluminium
Answer: (b) Gold
Explanation: Gold does not lose its
lustre when exposed to air, which is why it is used for making ornaments.
Unlike most metals, gold remains shiny without tarnishing.
12. What is the property of materials that describes
their ability to be compressed or scratched?
Solubility
Hardness
Appearance
Roughness
Answer: (b) Hardness
Explanation: Hardness is the property of
materials that determines how easily they can be compressed or scratched. Hard
materials like iron and diamond cannot be easily scratched, while soft
materials like wax or sponge can be compressed and scratched easily.
13. Which of the following substances is not soluble
in water?
Sugar
Salt
Sand
Vinegar
Answer: (c) Sand
Explanation: Sand is an insoluble
substance and does not dissolve in water, whereas sugar, salt, and vinegar are
soluble in water and form solutions.
14. What is the term used for liquids that do not mix
with each other?
Miscible liquids
Immiscible liquids
Soluble liquids
Insoluble liquids
Answer: (b) Immiscible liquids
Explanation: Immiscible liquids are
liquids that do not mix with each other and separate into distinct layers, such
as oil and water. Miscible liquids, on the other hand, mix completely to form
solutions.
15. Which of the following gases dissolve in water and
help aquatic plants and animals in photosynthesis and respiration?
Nitrogen
Hydrogen
Oxygen and Carbon dioxide
Methane
Answer: (c) Oxygen and Carbon dioxide
Explanation: Oxygen and carbon dioxide
dissolve in water, enabling aquatic plants and animals to perform
photosynthesis and respiration. These dissolved gases are essential for life in
aquatic ecosystems.
16. What is a universal solvent?
Vinegar
Water
Kerosene
Alcohol
Answer: (b) Water
Explanation: Water is called the
universal solvent because it dissolves a large number of substances, making it
essential for various biological and chemical processes, including its role in
the human body.
17. Which of the following is the hardest material?
Wax
Chalk
Diamond
Lead
Answer: (c) Diamond
Explanation: Diamond is one of the
hardest known substances and is extremely difficult to compress or scratch. It
is used in cutting tools because of its superior hardness.
18. What property of a material determines whether it
will float or sink in water?
Shape
Volume
Density
Hardness
Answer: (c) Density
Explanation: The ability of a material
to float or sink in water depends on its density. If the density of the
material is less than that of water, it will float. If it is greater, it will
sink.
19. Why does a metal ship float on water even though
it is made of metal, which normally sinks?
The density of metal decreases when shaped into a ship
The shape of the ship allows it to displace enough
water to stay afloat
The ship is made of a special type of metal
Ships have internal heat that keeps them afloat
Answer: (b) The shape of the ship allows
it to displace enough water to stay afloat
Explanation: Even though metal has a
high density, the shape of a ship allows it to displace enough water, reducing
its overall density compared to water, which allows it to float.
20. Which of the following is an example of a
translucent material?
Clear glass
Wood
Ground glass
Iron
Answer: (c) Ground glass
Explanation: Translucent materials allow
some light to pass through but do not provide a clear image. Ground glass is a
good example of a translucent material.
21. Which of the following materials would be
classified as opaque?
Clear water
Plastic wrap
Cardboard
Transparent glass
Answer: (c) Cardboard
Explanation: Opaque materials do not
allow any light to pass through them. Cardboard is an opaque material, meaning
objects cannot be seen through it.
22. Why are cooking vessels made of metals but their
handles made of materials like Bakelite?
Metals do not heat up quickly
Bakelite is stronger than metal
Metals are good conductors of heat, while Bakelite is
a poor conductor of heat
Bakelite conducts heat better than metal
Answer: (c) Metals are good conductors
of heat, while Bakelite is a poor conductor of heat
Explanation: Metals conduct heat
efficiently, which helps in cooking, while Bakelite, being a poor conductor of
heat, is used for handles to prevent them from getting too hot to touch.
23. Which of the following materials is a good
conductor of electricity?
Rubber
Copper
Plastic
Wood
Answer: (b) Copper
Explanation: Copper is a metal and a
good conductor of electricity. Materials like rubber, plastic, and wood are
poor conductors and are often used as insulators.
24. What is the term used for materials that are not
attracted by a magnet?
Magnetic materials
Non-magnetic materials
Conductors
Insulators
Answer: (b) Non-magnetic materials
Explanation: Non-magnetic materials,
such as wood, plastic, and rubber, are not attracted to magnets. Magnetic
materials, like iron, cobalt, and nickel, are attracted to magnets.
25. What is the name of the property that allows
certain materials to float on water?
Transparency
Floatation
Conductivity
Magnetic property
Answer: (b) Floatation
Explanation: Floatation is the property
of materials that determines whether they float on water. This is influenced by
the density of the material compared to the density of the water.
26. Which of the following substances is an immiscible
liquid when mixed with water?
Vinegar
Glycerine
Cooking oil
Lemon juice
Answer: (c) Cooking oil
Explanation: Cooking oil does not mix
with water and forms a separate layer when kept undisturbed. It is an example
of an immiscible liquid.
28. What is matter?
Anything that has color and shape
Anything that has mass and occupies space
Only solid substances
Substances that dissolve in water
Answer: (b) Anything that has mass and
occupies space
Explanation: Matter is defined as
anything that has mass and occupies space. This includes solids, liquids, and
gases.
29. What is lustre?
The roughness of a material
The hardness of a material
The shiny appearance of materials
The softness of a material
Answer: (c) The shiny appearance of
materials
Explanation: Lustre refers to the shiny
or glossy appearance that some materials, especially metals like gold and
silver, exhibit.
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