HYDROSPHERE-8th Standard Social Science Notes


l. Fill in the blanks with suitable words:

1.The average depth of the continental shelf is _______

2.One fathom is equal to ________ft.

3.The deepest place in the Pacific Ocean is __________

4.The average salinity of the ocean water is __________

5. ___________ tides occur during full moon.

Ans: (1) 100 fathoms (2) six (3) the Challenger deep of Mariana Trench (4) 35 parts of 1000 (35/°°°) PPT (5) Spring

II. Answer the following questions:

1. What is hydrosphere?

Ans: 71% of the total area of the Earth is surrounded by water. This is called hydrosphere.

2.Mention the four major parts of the ocean floor.

Ans: The four major parts of the ocean floor are –

(1) Continental Shelf

(2) Continental slope

(3) The Deep sea plain and

(4) The Ocean deep.

3.State the difference between ocean currents and tides.

Ans: Ocean currents are the regular movement of ocean water from one region to another.

Tides are the periodic rise and fall in the sea or ocean level.

4.Distinguish between spring tide and neap tide.

Ans: Spring tide: Spring tide takes place when the earth, the moon and the sun are in the same straight line. E.g. New Moon and Full Moon. When the spring tides take place, high tides are the highest and the low tides are the lowest.

Neap Tide: Neap tides occur on the first quarter and last quarter days in the phase of the Moon. During neap tides the sun and the earth are in the same straight line and moon in the right angle to the earth. In this type of tides the high tides are not very high and low tides are not very low.

5.How can we conserve the oceans?

Ans: We can conserve oceans through following methods:,
(1) Oil transportation should be done through pipelines.

(2) Nuclear waste should not be dumped into sea or ocean.

(3) Petro-chemical industries in the coastal regions must avoid dumping effluents into the sea or ocean.

(4) Dumping of any waste near the ports and harbours must be controlled.

(5) Ore deposition and mineral exploitation along the coast must be controlled.

(6) Exploitation and destruction of beaches must be controlled.

III Match the following:


1.Fathom (a) deep sea plain

2.Oyashio (b) eastern coast of USA

3.Gulf stream (c) cold current

4.Sea mounts (d) Indian ocean current

5.Agulhas current (e) depth of ocean

Ans: 1-e, 2-c, 3-b, 4-a, 5-d.

IV. Define the following:

1. Continental shelf:- Continental shelf is the shallow area along the sea coast. This part is bordered by the sea coast on one side and continental slope on the other side. The average depth of the continental shelf is 100 fathoms.

2.Salinity: Salinity is the percentage of salts dissolved in the sea or ocean water. The average salinity of the ocean water is 35 parts per thousand.

3.Warm and cold currents: Warm currents originate and flow from the equatorial regions to sub-polar regions.

Cold currents originate in the Polar Regions and flow towards the equatorial region.

4.High tide and Low tide: High tide, also known as Flood tide and Low tide also known as Ebb tide. On the water bodies of the earth there are alternate high tides and low tides. Between one high tide and a low tide the time is 6 hrs, 13 minutes. Between one high tide and another, the time gap is 12 hrs, 26 minutes. In 24 hrs, 52 minutes there are 2 high tides and 2 low tides.

5.Benguela current: Benguela current is the cold currents of South Atlantic Ocean.

6. Tides: Tides are the periodic rise and fall in the sea or ocean level. They occur due to gravitational attraction by the moon, gravitational force by the sun, rotation of the earth and centrifugal force of the earth.

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