8th Std Social Science Term 1 Solution | Lesson.7 Hydrologic Cycle

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Lesson.7 Hydrologic Cycle

8th Std Social Science Guide in English | Hydrologic Cycle

Lesson.7 Hydrologic Cycle

I. Choose the correct answer

1. The process in which the water moves between the oceans, atmosphere and land is called

  1. River Cycle
  2. Hydrologic Cycle
  3. Rock Cycle
  4. Life Cycle

Ans : Hydrologic Cycle

2. The percentage of fresh water on the earth is

  1. 71
  2. 97
  3. 2.8
  4. 0.6

Ans : 2.8

3. The process of changing of water from gaseous to liquid form is known as

  1. Condensation
  2. Evaporation
  3. Sublimation
  4. Rainfall

Ans : Condensation

4. Water that flows in the sub-soil or through the ground into the streams, rivers, lakes and oceans is termed as

  1. Condensation
  2. Evaporation
  3. Transpiration
  4. Runoff

Ans : Runoff

5. The evaporation of water from the leaves ofplants is called

  1. Transpiration
  2. Condensation
  3. Water vapour
  4. Precipitation

Ans : Transpiration

6. Water that is good enough to drink is called

  1. Groundwater
  2. Surface water
  3. Potable water
  4. Artesian water

Ans : Groundwater

II. Fill in the Blanks.

1. The degree of water vapour present in the atmosphere is known as__________.

Ans : humidity

2. There are _____________ phases in the water cycle.

Ans : Six

3. The falling of water towards the earth surface from atmosphere in any form is known as ____________.

Ans : Rain

4. The precipitation with the rain drop size of<0.5mm in diameter is known as _______________.

Ans : drizzle

5. Mist is denser than _______________.

Ans : Fog

III. Match the following

1. VegetationClouds
2. CondensationSleet
3. Snow and rain dropsAt the surface
4. InfiltrationTranspiration
 Ans : 1 – B, 2 – C, 3 – D, 4 – A

IV. Choose the correct statement

1. Evaporation refers to

I. The process in which the gaseous form of water changes in to liquid form.

II. It refers to the process in which the liquid form of water changes into gaseous form.

III. Water boils at 100oC temperature but, it actually begins to evaporate at 0oC.

IV. It is responsible for the formation of clouds.

  1. I, IV and V are correct
  2. II only correct
  3. II and III are correct
  4. All are correct

Ans: II and III are correct

IV. State true or false :

1.Water boils at 212°F temperature but, it begins to evaporate at 32°F.

Ans : True

2. Mist is not the tiny droplets of water hanging in the air.

Ans : False

3. The sub – surface runoff is usually referred as interflow.

Ans : True

VI. Answer in brief

1. Write a short note on aquifer.

An aquifer is an underground layer of water – bearing rock.

2. Define “hydrological cycle”.

Hydrologic cycle is a global sun – driven process where water is transported from oceans to atmosphere, from atmosphere to land and from land back to oceans.

3. How is the dew formation takes place?

Dew is a water droplet formed by the condensation of water vapour on a relatively cold surface of an object. It forms when the temperature of an object drops below the dew point temperature.

4. Write a short note on surface run – off.

Surface Runoff is the portion of rainfall, which enters the stream immediately after the rainfall. It occurs, when the rainfall is longer, heavier and exceeds the rate of infiltration. In this condition the excess water makes a head over the ground surface, which tends to move from one place to another following land gradient and is known as overland flow. When the overland flow joins the streams, channels or oceans, it is termed as surface runoff or surface flow.

VII. Give reasons

1. Infiltration of water is low in the region of non – porous soil.

Water entering the soil at the surface of the ground is termed as infiltration. Infiltration allows the soil temporarily to store water, the rate of infiltration is influenced by the physical characteristics of the soil, vegetative cover, moisture content of the soil, soil temperature and rainfall intensity.

2. Fresh water is less on the earth.

Most of the water on the earth is saline and is found in seas and oceans, which constitutes about 97.2%.

3. Snowfall is common in the polar region and mountainous regions.

  • The precipitation in the form of powdery mass of ice is known as snowfall.
  • Often water vapour in a cloud is converted directly into snow pieces due to lowering of temperature.
  • It is common in the polar and high mountainous regions.

VIII. Answer in a paragraph

1. Explain the different stages involved in the hydrological cycle.

The three important phases of the hydrologic cycle are:

  1. Evapotranspiration,
  2. Precipitation and
  3. Runoff.

1. Evapotranspiration:

It is defined as the total loss of water from the earth through evaporation from the surface water bodies and the transpiration from vegetation. In cropped area, it is difficult to determine the evaporation and transpiration separately. Therefore it is collectively called as evapotranspiration.

2. Precipitation:

It refers to all forms of water that fall from clouds and reaches the earth’s surface. For the occurrence of precipitation, cloud droplets or ice crystals must grow heavy enough to fall through the air. When the droplets grow large in size, they tend to all. While moving down, by collecting some small droplets, they become heavy enough to fall out of the cloud as raindrops.

3. Runoff:

Runoff is the water that is pulled by gravity across land’s surface. It replenishes groundwater and surface water as it percolates into an aquifer (it is an underground layer of water – bearing rock) or moves into a river, stream or watershed. It comes from unabsorbed water from rain, snowmelt, irrigation or other sources, comprising a significant element in the water cycle as well as the water supply when it drains into a watershed. Runoff is also a major contributor to the erosion which carves out canyons, gorges and related landforms.

2. Distinguish between evaporation and transpiration.

Evaporation:

  • Process in which the liquid form of water changes into gaseous form.
  • Rate of evaporation is affected by temperature, Areal extent of surface water, wind and the atmospheric humidity.
  • 90% moisture in the atmosphere is contributed through evaporation.

Transpiration:

  • Process by which the water content in the plant is released into the atmosphere in the form of water vapour.
  • Rate of Transpiration is affected temperature, wind and humidity.
  • 10% moisture is contributed through Transpiration.

3. Give a detailed explanation on different forms of precipitation.

Forms of Precipitation:

The form of precipitation in a region depends on the kind of weather or the climate of the region. Common types of precipitation include rain, sleet, freezing rain, hail and snow.

Rain:

The precipitation in the form of water droplets is called rain. The precipitation in which the size of rain drops are <0.5 mm in diameter is known as drizzle and the rain drops with >0.5 mm in diameter is known as rain. Generally drizzle takes place from stratus clouds.

Sleet:

The precipitation which takes place in the form of mixture of water droplets and tiny particles of ice(5mm in diameter) is known as sleet. Sometimes raindrops fall through a layer of air below 0°C. As they fall, the raindrops freeze into solid particles of ice. So, the mixture of water droplets and ice particles would fall on the earth surface.

Freezing Rain:

At other times raindrops falling through cold air near the ground do not freeze in the air. Instead, the raindrops freeze when they touch a cold surface. This is called freezing rain.

Hail:

The precipitation which consists of round pellets of ice which are larger than 5 mm in diameter is called hail or hailstones. A hailstone starts as an ice pellet inside a cold region of a cloud.

Snow:

Often water vapour in a cloud is converted directly into snow pieces due to lowering of temperature. The precipitation in the form of powdery mass of ice is known as snowfall. It is common in the polar and high mountainous regions.

4. Explain the run – off and its types.

Runoff is the water that is pulled by gravity across land’s surface. It replenishes groundwater and surface water as it percolates into an aquifer (it is an underground layer of water-bearing rock) or moves into a river, stream or watershed.

Types of Runoff:

Based on the time interval between the instance of rainfall and generation of runoff, the runoff may be classified into following three types

1. Surface Runoff:

It is the portion of rainfall, which enters the stream immediately after the rainfall. It occurs, when the rainfall is longer, heavier and exceeds the rate of infiltration. In this condition the excess water makes a head over the ground surface, which tends to move from one place to another following land gradient and is known as overland flow. When the overland flow joins the streams, channels or oceans, it is termed as surface runoff or surface flow.

2. Sub – Surface Runoff:

The water that has entered the subsoil and moves laterally without joining the water-table to the streams, rivers or oceans is known as sub- surface runoff. The sub – surface runoff is usually referred as interflow.

3. Base Flow:

It is a flow of underground water from a saturated ground water zone to a water channel. It usually appears at a downstream location where the channel elevation is lower than the groundwater table. Groundwater provides the stream flow during dry periods of small or no precipitation.

 

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