कक्षा 7 सामाजिक विज्ञान
विषय :
सामाजिक विज्ञान (भूगोल – हमारा पर्यावरण)
अध्याय:-5 (जल)
अभ्यास:-
1 . निम्न प्रश्नों के उत्तर दीजिए:-
(क) वर्षण क्या है ?
उत्तर :- वायुमण्डलीय जल के संघनित होकर
किसी भी रूप में पृथ्वी की सतह पर वापस आने को वर्षण कहते हैं। वर्षण के कई रूप हो
सकते हैं,
जैसे
वर्षा,
फुहार, हिमवर्षा, हिमपात। यह वर्षा, ओलावृष्टि, बर्फ या बर्फ के रूप में
पृथ्वी पर पानी का जमाव है।
(ख) जल चक्र क्या है ?
उत्तर :- सूर्य के ताप के कारण जल
वाष्पित हो जाता है और ठंडा होने पर जलवाष्प संघनित होकर बादलों का रूप ले लेता
है। यहाँ से यह वर्षा, हिम अथवा सहिम वृष्टि के रूप
में धरती या समुद्र पर नीचे गिरता है। जिस प्रक्रम में जल लगातार अपने स्वरूप को
बदलता रहता है और महासागरों, वायुमंडल एवं धस्तों के बीच
चक्कर लगाता रहता है, उस को जल चक्र कहते है।
(ग) लहरों की ऊँचाई प्रभावित
करने वाले कारक कौन – से है ?
उत्तर :- लहरों की ऊँचाई को प्रभावित
करने वाले कारक निम्नलिखित है, जैसे:- तूफ़ान में तेज वायु के
कारण,
सूर्य
एवं चन्द्रमा के शक्तिशाली गुरुत्वाकर्षण बल के कारण, जल के नीचे भूस्खलन के कारण, ज्वालामुखी के उद्गार के कारण।
(घ) महासागरीय जल की गति को
प्रभावित करने वाले कारक कौन –
से हैं ?
उत्तर :- महासागरीय जल की गति को
प्रभावित करने वाले कारक निम्नलिखित है, जैसे:- समुन्द्र के नीचे या आस
–
पास
भूकंप के कारण, पानी के तापमान के ज्यादा होने के कारण, ज्वालामुखी के विस्फोट के
कारण।
(ड़) ज्वार –
भाटा क्या है तथा ये कैसे उत्पन्न होते है
?
उत्तर :- दिन में दो बार नियम से
महासागरीय जल का उठना एवं गिरना ‘ज्वार – भाटा ‘ कहलाता है। जब सर्वाधिक ऊँचाई
तक उठकर जल,
तट के
बड़े हिस्से को डुबो देता है, तब उसे ज्वार कहते हैं। जब जल
अपने निम्नतम स्तर तक आ जाता है एवं तट से पीछे चला जाता है, तो उसे भाटा कहते हैं। सूर्य
एवं चंद्रमा के शक्तिशाली गुरुत्वाकर्षण बल के कारण पृथ्वी की सतह पर ज्वार – भाटे आते हैं। जब पृथ्वी का जल
चंद्रमा के निकट होता है उस समय चंद्रमा के गुरुत्वाकर्षण बल से जल अभिकर्षित होता
है,
जिसके
कारण उच्च ज्वार आते हैं।
(च) महासागरीय धाराएँ क्या है ?
उत्तर :- महासागरीय धाराएँ, निश्चित दिशा में महासागरीय
सतह पर नियमित रूप से बहने वाली जल की धाराएँ होती हैं। महासागरीय धाराएँ गर्म या
ठंडी हो सकती हैं। गर्म महासागरीय धाराएँ, भूमध्य रेखा के निकट उत्पन्न
होती हैं एवं ध्रुवों को ओर प्रवाहित होती हैं। ठंडी भाराएँ, ध्रुवों या उच्च अक्षांशों से
की उष्णकटिबंधीय या निम्न अक्षांशों की ओर प्रवाहित होती हैं।
2. कारण बताइए :-
(क) समुंद्री जल नमकीन होता है।
उत्तर :- समुंद्र में नदियाँ अपना जल
बहाकर लाती हैं। ये बड़ी मात्रा में खनिज लवणों को बहाकर समुंद्र में लाती है।
समुंद्र में जल का नियमित रूप से भारी मात्रा में वाष्पीकरण होता रहता है। लवणीय
पदार्थों का वाष्पीकरण नहीं होता। इसलिए समुंद्र का जल नमकीन हो जाता हैं।
(ख) जल की गुणवत्ता का हास हो
रहा है।
उत्तर :- मनुष्य की वजह से जल की गुणवता
के ह्रास होने के निम्नलिखित कारण हैं:-
1. नदियों में कूड़ा – करकट फेंक दिया जाता है ।
2. उद्योगों से रसायन व प्रदूषित
जल की निकासी नदियों में होती है।
3. नदियों में मानव की जली तथा
अधजली लाशें,
जानवरों
के शव,
आदि
फेंक दिए जाते हैं।
4. खेतों में कीटनाशकों तथा
उर्वरकों के हानिकारक तत्त्व भी पानी में मिलते रहते हैं।
3. सही (√)
उत्तर चिह्नित कीजिए :-
(क) वह प्रक्रम जिस में जल
लगातार अपने स्वरूप को बदलता रहता है और महासागर,
वायुमंडल एवं स्थल के बीच चक्कर लगाता
रहता है।
(i)
जल चक्र
(ii)
ज्वार – भाटा
(iii) महासागरीय धाराएँ
उत्तर:- जल चक्र
(ख) सामान्यत: गर्म
महासागरीय धाराएँ उत्पन्न होती हैं
(i)
ध्रुवों
के निकट (ii)
भूमध्य
रेखा के निकट (iii) दोनों में से कोई नहीं
उत्तर :- भूमध्य रेखा के निकट
(ग) दिन में दो बार नियम से
महासागरीय जल का उठना एवं गिरना कहलाता है ?
(i)
ज्वार – भाटा (ii) महासागरीय धाराएँ (iii) तरंग
उत्तर :- ज्वार – भाटा
4. निम्नलिखित स्तंभों को मिलाकर
सही जोड़े बनाइए:-
(क) कैस्पियन सागर (i)
विशालतम
झील
(ख) ज्वार-भाटा (ii) जल में आवधिक चढ़ाव एवं उतार
(ग) सुनामी
(iii) तीव्र
भूकंप तरंगें
(घ) महासागरीय धाराएँ (iv) निश्चित मार्ग में प्रवाहित
होने वाली जल धाराएं
(v)
जल चक्र
उत्तर :-
(क) कैस्पियन सागर (i)
विशालतम
झील
(ख) ज्वार भाटा (ii)
जल में
आवधिक चढ़ाव एवं उतार
(ग) सुनामी (iii)
तीव्र
भूकंप तरंगें
(घ) महासागरीय धाराएँ (iv) निश्चित मार्ग में प्रवाहित
होने वाली जल धाराएँ
Chapter 5
Water
Q. 1. Answer the following questions briefly.
(a) What is precipitation?
(b) What is the water cycle?
(c) What are the factors affecting the height
of the waves?
(d) Which factors affect the movement of ocean
water?
(e) What are tides and how are they caused?
(f) What are ocean currents?
Ans.
(a) Falling of
moisture in the form of rainfall, snow, fog, sleet, and hailstone is termed as
precipitation.
(b) The water cycle is the process by which water continually changes its form
and circulates between oceans, atmosphere, and land.
(c) Winds, earthquakes, volcanic eruption, or underwater landslides are the
factors affecting the height of the waves. The stronger the wind blows, the
bigger the wave becomes.
(d) Temperature, winds, the gravitational pull of the sun, the earth, and the
moon; warm and cold currents are the factors that affect the movement of ocean
water.
(e) Tides are the rhythmic rise and fall of ocean water that occurs twice in a
day. The strong gravitational pull exerted by the sun and the moon on the
earth’s surface cause the tides.
(f) Ocean currents are streams of water flowing constantly on the ocean surface
in definite directions.
Q. 2. Give reasons:
(a) Ocean water is salty.
(b) The quality of water is deteriorating.
Ans.
(a) The water of the
oceans is salty as it contains a large amount of dissolved salts.
(b) Water is being used injudiciously. Whatever potable water is available, its
quality is not good. It is because industrial effluents and untreated water of
industries get mixed into streams and rivers. Sewerage water also gets mixed
into these water bodies. As a result, the quality of water is deteriorating day
by day.
Q. 3. Tick the correct
answer.
(a)
The process by which water continually changes its form and circulates between
oceans, atmosphere and land
(i) Water cycle
(ii) Tides
(iii) Ocean currents.
(b) Generally the warm
ocean currents originate near
(i) Poles
(ii) the Equator
(iii) None of these.
(c) The rhythmic rise
and fall of ocean water twice in a day is called
(i) Tide
(ii) Ocean current
(iii) Wave
Ans.
(a)—(i), (b)—(ii), (c)—(i)
Q. 5. For Fun
Be
a Detective
1. The name of one river is hidden in each of the sentences below. Spot it.
Example: Mandira, Vijayalakshmi and Surinder are my best friends
Ans. Ravi
(a) The snake charmer’s bustee, stables where horses are housed, and the piles
of wood, all caught fire accidentally. (Hint: Another name for River
Brahmputra)
(b) The conference manager put pad, material for reading and a pencil for each
participant. (Hint: A distributary on the Ganga-Brahmputra delta)
(c) Either jealousy or anger cause a person’s fall (Hint: Name of a juicy
fruit!)
(d) Bhavani germinated the seeds in a pot (Hint: Look for her in West Africa)
(e) “I am a zonal champion now” declared the excited athlete. (Hint: The river
that has the biggest basin in the world)
(f) The tiffin box rolled down and all the food fell in dusty potholes.
(Hint: Rises in India and journeys through Pakistan)
(g) Malini leaned against the pole when she felt that she was going to faint.
(Hint: Her delta in Egypt is famous)
(h) Samantha mesmerised everybody with her magic tricks. (Hint: London is
situated on her estuary)
(i) “In this neighbourhood, please don’t yell! Owners of these houses like to
have peace. Warned my father when we moved into our new flat”. (Hint: colour!)
(j) ‘Write the following words’, Marc! “On”, “go”, “in”……….. said
the teacher to the
little boy in KG Class. (Hint: Rhymes with ‘bongo’)
Now make some more on your own and ask your classmates to spot the hidden name.
You can do this with any name: that of a lake, mountains, trees, fruits, school
items, etc.
TAns. eesta, (b) Padma, (c) Orange, (d) Niger, (e) Amazon,
(f) Indus, (g) Nile,
(h) Thames, (i) yellow,(j) Conga.
Carry on Detective
2. With the help of an
atlas, draw each river which you discovered in For fun (0, on
an
outline map of the world.
Ans. Do yourself.
VERY
SHORT ANSWER TYPE QUESTIONS
Q.1. What is a
terrarium?
Ans. It is an artificial
enclosure for keeping small house plants. .
Q.2. Which type of
water do the ocean bodies and the seas contain?
Ans. They contain salty
water.
Q.3. What do you mean
by salinity? [V. Imp.]
Ans. Salinity is the
amount of salt in grams present in 1000 grams of water.
Q.4. What is the
average salinity of the oceans?
Ans. The average salinity
of the oceans is 35 parts per thousand.
Q.5. What is the
salinity of the Dead sea?
Ans. The salinity of
the Dead sea is 45 parts per thousand.
Q.6. Why do swimmers
float in the Dead Sea?
Ans. Swimmers float in
the Dead sea because the increased salt content makes it dense.
Q.7. What is the
significance of World Water Day?
Ans. On the occasion of
World Water Day (22nd March) the need to conserve water is reinforced in
different ways.
Q. 8. What is a
Tsunami? [V. Imp.]
Ans. Tsunami is a
Japanese word that means ‘Harbour Waves’ as the harbors get destroyed whenever
there is a Tsunami.
Q.9- What happens
during high Ode? [Imp.]
Ans. During high
tide, waves rise high and water covers much of the shore.
Q. 10. What happens
during low tide?
Ans. During low tide
waterfalls to its lowest level and recedes from the shore.
Q. 11. How are
tides caused?
Ans. The strong
gravitational pull exerted by the sun and the moon on the earth’s surface cause
tides.
Q.12. Name one warm
current and one cold current.
Ans. Warm current —
The Gulf Stream
Cold current — The Labrador Ocean current.
Q. 13. What
happened to the Indira point during the tsunami of 2004?
Ans. It got submerged.
SHORT
ANSWER TYPE QUESTIONS
Q.1. How are spring
and neap tides formed? [V. Imp.]
Ans. During the full
moon and new moon days, the sun, the moon, and the earth are in the same line
and the tides are highest. These tides are called spring tides. But when the
moon is in its first and last quarter, the ocean waters get drawn in diagonally
opposite directions by the gravitational pull of the sun and earth resulting in
low tides. These tides are called neap tides.
Q.2. How are high
tides important?[V. Imp.]
Ans. High tides are
important for various reasons:
·
They help in navigation
·
They raise the water level close to the
shores. This helps the ships to arrive at the harbour more easily.
·
The high tides also help in fishing.
Much more fish come closer to the shore during the high. This enables the
fisherman to get a plentiful catch.
·
The rise and fall of water due to tides
is being used to generate electricity in some places.
Q.3. What are the
waves? Write a short note on it
Ans. Waves are the
rise and fall of the water on the surface of the ocean. Waves are formed when
winds scrape across the ocean surface. The stronger the wind blows, the bigger
the wave becomes. During the storm, the winds blow at very high speed and
therefore huge waves are formed. These waves are very strong, hence very
destruction. They may cause huge devastation.
Q.4. Write a brief
note on Tsunami. [Imp.]
Ans. Tsunami is a Japanese word that means ‘harbour waves’ as the harbours get
destroyed whenever there is a tsunami. An earthquake, a volcanic eruption or
underwater landslides can shift large amounts of ocean water. As a result
tsunami occurs which may be as high as 15 m. The tsunami of 2004 is still in
our minds. It caused huge death and destruction in the coastal areas of India.
The Indira Point in the Andaman and Nicobar Islands got submerged after the
tsunami.
Q.5. Write a note on
the importance of water. [V. Imp.]
Ans. Water is life.
Without water, we can not think of life. Its scarcity may create numerous
problems but its absence would definitely lead to the non-existence of all the
living beings on the earth. It is a precious resource of nature. We drink water
whenever we feel thirsty. We use water in numerous activities such as washing
clothes, cleaning house floors, watering the garden, etc. Industries also need
water for their functioning. Thus, water is very essential and therefore we
must conserve it. Our careless use of water has created several problems.
Whatever water is there, it is not of good quality. We should think about the
ways of its conservation for our own sake.
Q.6. Explain the water
cycle with a neat and labelled
diagram.
[V. Imp.]
Ans. The sun’s heat
causes evaporation of water, flowing down to stream or drains into water
vapour. When the water vapour cools down, it condenses and forms clouds. These
clouds, when become too heavy to float, start falling on the land or sea in the
form of rain, snow, or sleet. Thus, the process by which water continually
changes its form and circulates between oceans, atmosphere, and land is known
as the water cycle.
LONG
ANSWER TYPE QUESTIONS
Q.1. Give an account
of ocean currents. [Imp.]
Ans. Ocean currents
are streams of water flowing constantly on the ocean surface in definite
directions. The ocean currents may be warm or cold. The warm ocean currents
originate near the equator and move towards the poles. The cold current carries
water from polar or higher latitudes to tropical or lower latitudes. For
example, the Labrador Ocean current is a cold current while the Gulf Stream is
a warm current.
The
ocean current influences the temperature conditions of the area. Warm currents
bring about warm temperatures over the land surface. The areas where the warm
and cold currents meet provide the best fishing grounds of the world. For
example seas around Japan and the eastern coast of North America. The areas
where a warm and cold current meet also experience foggy weather and therefore
navigation becomes difficult.
Q.2. How do we
classify ocean movements? Explain. [V. Imp.]
Ans. Ocean movements
can be classified into waves, tides, and currents.
When
the water on the surface of the ocean rises and falls alternately, they are
called waves. Waves are formed when winds scrape across the ocean surface. The
stronger the wind blows, the bigger the wave becomes.
The
rhythmic rise and fall of ocean water twice in a day is known as a tide. Tides
may be high or low. It is high tide when water covers much of the shore by
rising to its highest level. It is low tide when waterfalls to its lowest level
and recedes from the shore. Tides are caused due to the strong gravitational
pull exerted by the sun and moon on the earth’s surface. High tides help in
navigation and fishing. The rise and fall of water due to tides is being used
to generate electricity in some places.
Ocean
currents. These are streams of water flowing constantly on the ocean surface in
definite directions. The ocean currents may be warm such as the Gulf Stream and
cold such as the Labrador Ocean current. The areas where the warm and cold
currents meet provide the best fishing ground of the world. For example, seas
around Japan and the Eastern Coast of North America.
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