Samacheer Kalvi Class 8 Social Science Solutions Chapter 3 Hydrologic Cycle

I. Choose the Correct Answer.

Question 1. The process in which the water moves between the oceans, atmosphere and land is called
(a) River Cycle
(b) Hydrologic Cycle
(c) Rock Cycle
(d) Life Cycle
Answer: (b) Hydrologic Cycle
In simple words: The hydrologic cycle, also known as the water cycle, describes how water constantly moves around the Earth. It involves water evaporating from oceans, forming clouds in the atmosphere, falling as rain or snow onto land, and then flowing back to the oceans.

🎯 Exam Tip: Remember that the hydrologic cycle is a continuous, natural process essential for life on Earth. Key terms to recall are evaporation, condensation, precipitation, and runoff.

Question 2. The percentage of fresh water on the earth is
(a) 71
(b) 97
(c) 2.8
(d) 0.6
Answer: (c) 2.8
In simple words: Only a very small part of all the water on Earth is fresh water, about 2.8%. Most of the water is salty water found in oceans.

🎯 Exam Tip: It's important to know the distribution of water on Earth, especially the small percentage of freshwater available for human use.

Question 3. The process of changing of water from gaseous to liquid form is known as
(a) Condensation
(b) Evaporation
(c) Sublimation
(d) Rainfall
Answer: (a) Condensation
In simple words: When water vapor (gas) in the air gets cold, it turns back into tiny liquid water droplets. This process is called condensation. This is how clouds form in the sky.

🎯 Exam Tip: Clearly differentiate between condensation (gas to liquid) and evaporation (liquid to gas) in the water cycle.

Question 4. Water that flows in the sub-soil or through the ground into the streams, rivers, lakes and oceans is termed as
(a) Condensation
(b) Evaporation
(c) Transpiration
(d) Runoff
Answer: (d) Runoff
In simple words: Water that moves over the land surface or through the soil towards rivers, lakes, and oceans is called runoff. This water might soak into the ground or flow directly into larger water bodies.

🎯 Exam Tip: Understand that runoff includes both surface flow and sub-surface flow that eventually contributes to larger water bodies.

Question 5. The evaporation of water from the leaves of plants is called
(a) Transpiration
(b) Condensation
(c) Water vapour
(d) Precipitation
Answer: (a) Transpiration
In simple words: Plants release water vapor into the air from their leaves, a process called transpiration. This is a bit like sweating for plants.

🎯 Exam Tip: Remember that transpiration is a specific type of evaporation, focusing on water release from plants into the atmosphere.

Question 6. Water that is good enough to drink is called
(a) Groundwater
(b) Surface water
(c) Potable water
(d) Artesian water
Answer: (c) Potable water
In simple words: Water that is safe to drink and clean enough for cooking is known as potable water. It must meet certain safety standards.

🎯 Exam Tip: Potable water implies it's safe for consumption, which is different from just "fresh water" as freshwater might still need treatment to be safe.

II. Fill in blank:

Question 1. The degree of water vapour present in the atmosphere is known as weather.
Answer: The degree of water vapour present in the atmosphere is known as humidity.
In simple words: The amount of water gas in the air is called humidity. Higher humidity makes the air feel sticky.

🎯 Exam Tip: Humidity is a key factor in weather patterns, directly affecting temperature and precipitation.

Question 2. There are Three phases in the water cycle.
Answer: There are three phases in the water cycle.
In simple words: The water cycle has three main steps: water evaporating, forming clouds (condensation), and then falling back to Earth (precipitation).

🎯 Exam Tip: Be sure to name the three main phases of the water cycle: evaporation, condensation, and precipitation.

Question 3. The falling of water towards the earth surface from the atmosphere in any form is known as Precipitation
Answer: The falling of water towards the earth surface from the atmosphere in any form is known as precipitation.
In simple words: When water falls from the sky to the ground, no matter if it's rain, snow, or hail, it is called precipitation. This is how water returns to Earth's surface from the atmosphere.

🎯 Exam Tip: Precipitation is the umbrella term for all forms of water falling from the atmosphere, not just rain.

Question 4. The precipitation with a rain drop size of less than 0.5mm in diameter is known as drizzle.
Answer: The precipitation with a rain drop size of less than 0.5mm in diameter is known as drizzle.
In simple words: Very tiny raindrops, smaller than 0.5 millimeters, are called drizzle. It's a light and fine kind of rain.

🎯 Exam Tip: Knowing specific measurements like droplet size can help distinguish between different forms of precipitation.

Question 5. Mist is denser than Clouds.
Answer: Mist is denser than fog.
In simple words: Mist is thicker and heavier than fog, meaning you can see a bit further through mist than through fog.

🎯 Exam Tip: Differentiate between mist, fog, and clouds based on density and visibility. Mist is often thinner than fog, not denser.

III. Match the following:

🎯 Exam Tip: For matching questions, understand the definition of each term to correctly pair them. Think about cause-and-effect relationships.

IV. Choose the correct statement:

Question 1. Evaporation refers to
I. The process in which the gaseous form of water changes into liquid form.
II. It refers to the process in which the liquid form of water changes into a gaseous form.
III. Water boils at 100°C temperature but, it actually begins to evaporate at 0°C.
IV. It is responsible for the formation of clouds.
(a) I, IV, and V are correct
(b) II only correct
(c) II and III are correct
(d) All are correct
Answer: (c) II and III are correct
In simple words: Evaporation is when liquid water turns into a gas. This can happen even at cold temperatures, not just boiling point. Evaporation itself does not form clouds, but the water vapor it creates is used to form clouds through condensation.

🎯 Exam Tip: Be precise with scientific definitions. Evaporation is liquid to gas, condensation is gas to liquid. Water can evaporate at temperatures below its boiling point.

V. State whether the following statements are True or False:

Question 1. Water boils at 212°F temperature but, it begins to evaporate at 32°F.
Answer: True
In simple words: Water boils at 212 degrees Fahrenheit, but it can start turning into vapor (evaporating) even at 32 degrees Fahrenheit. This shows evaporation can happen at much lower temperatures than boiling.

🎯 Exam Tip: Distinguish between boiling (rapid evaporation at a specific temperature) and evaporation (slow process occurring at any temperature above freezing).

Question 2. Mist is not the tiny droplets of water hanging in the air.
Answer: False
In simple words: Mist is actually made of tiny water droplets floating in the air. It looks like a light fog.

🎯 Exam Tip: Remember that mist, fog, and clouds all consist of tiny suspended water droplets, differing mainly in density and location.

Question 3. The sub-surface runoff is usually referred to as interflow.
Answer: True
In simple words: Water that flows just below the ground surface, but above the main groundwater level, is often called interflow. It's a type of runoff.

🎯 Exam Tip: Interflow is an important component of the hydrological cycle, contributing to streamflow, especially during and after rainfall events.

VI. Answer in brief:

Question 1. Write a short note on the aquifer.
Answer: An aquifer is a layer of rock or soil underground that can hold and transmit water. It acts like a natural reservoir for groundwater, storing water that has seeped down from the surface. These underground water sources are very important for drinking water and agriculture. Groundwater can be pumped from aquifers through wells.
In simple words: An aquifer is an underground rock or soil layer that holds water. It's like a big natural sponge that stores water beneath the ground.

🎯 Exam Tip: Focus on the definition of an aquifer as a water-bearing underground rock layer and its role in supplying groundwater.

Question 2. Define " hydrological cycle”.
Answer: The hydrological cycle is a global process driven by the sun, where water continuously moves. It involves water being transported from oceans to the atmosphere, from the atmosphere to land, and then from land back to oceans. This constant movement keeps water circulating around the Earth.
In simple words: The hydrological cycle is the continuous movement of water on, above, and below the Earth's surface, powered by the sun.

🎯 Exam Tip: Emphasize the continuous and sun-driven nature of the hydrological cycle and list its major stages.

Question 3. How is the dew formation takes place?
Answer: Dew is formed when water vapor in the air condenses into liquid water droplets on a relatively cold surface of an object. This happens when the object's temperature drops below the dew point temperature, which is the temperature at which the air becomes saturated with water vapor. The cold surface cools the air directly above it, causing the water vapor to change into liquid.
In simple words: Dew forms when the air cools down overnight, making the water vapor in the air turn into tiny water drops on cool surfaces like grass.

🎯 Exam Tip: Key elements for explaining dew formation are condensation, cold surfaces, and the dew point temperature.

Question 4. Write a short note on surface run-off
Answer: Surface runoff is the part of rainfall that flows into streams immediately after the rain. It occurs when rainfall is long, heavy, and exceeds the rate at which water can soak into the ground (infiltration). In this situation, the extra water creates a layer over the ground surface, moving downslope as overland flow. When this overland flow reaches streams, channels, or oceans, it is then called surface runoff or surface flow.
In simple words: Surface runoff is rainwater that flows over the land because the ground cannot absorb it fast enough. It then goes into rivers and other water bodies.

🎯 Exam Tip: Explain that surface runoff happens when precipitation intensity is greater than the soil's infiltration capacity, leading to water flowing over the land.

VII. Give reasons:

Question 1. Infiltration of water is low in the region of non-porous soil.
Answer: Infiltration of water is low in non-porous soil regions because these soils have very small spaces (pores) or are tightly packed. This makes it difficult for water to move through the soil and rock layers to form groundwater. Water cannot easily seep into these types of ground, so it tends to stay on the surface or run off instead.
In simple words: Water does not soak well into non-porous soil because it is packed tightly and has no room for water to get in.

🎯 Exam Tip: Emphasize the role of soil porosity (the amount of empty space in the soil) in determining the rate of water infiltration.

Question 2. Freshwater is less on the earth.
Answer: Most of the water on Earth is saline (salty) and is found in seas and oceans, making up about 97.2% of all water. Only a small fraction, roughly 2.8%, is freshwater. This small amount of freshwater is crucial for human consumption and ecosystems.
In simple words: Most of Earth's water is salty ocean water. Only a tiny bit, around 2.8%, is fresh water, which is what we need to drink.

🎯 Exam Tip: Remember the approximate percentages of saline versus freshwater on Earth and where each type is primarily found.

Question 3. Snowfall is common in the polar region and mountainous regions.
Answer: Snowfall is common in polar and mountainous regions because in these areas, water vapor in clouds often turns directly into snow particles due to very low temperatures. The cold air masses and high altitudes in these regions provide the necessary conditions for ice crystals to form and fall as snow, rather than rain.
In simple words: Snow falls a lot in very cold places like the poles and high mountains because the air there is freezing, which turns water vapor into snow instead of rain.

🎯 Exam Tip: Connect snowfall to specific temperature conditions and geographical features like polar regions and high altitudes.

VIII. Answer in a paragraph:

Question 1. Explain the different stages involved in the hydrological cycle.
Answer: The three main stages of the hydrologic cycle are:
• **Evapotranspiration:** This is the total water lost from the Earth's surface through evaporation from water bodies and transpiration from plants. It's often hard to measure evaporation and transpiration separately, so they are grouped together.
• **Precipitation:** This refers to all forms of water (like rain, snow, hail) that fall from clouds and reach the Earth's surface. For precipitation to happen, tiny cloud droplets or ice crystals must grow large enough to fall through the air.
• **Runoff:** Runoff is the water that flows over the land due to gravity. It helps refill groundwater and surface water. It includes water from rain, melted snow, or irrigation that doesn't soak into the ground. Runoff is also a big cause of erosion, shaping the land over time.
In simple words: The water cycle has three main steps: evapotranspiration (water turning into vapor from land and plants), precipitation (water falling as rain or snow), and runoff (water flowing over the land).

🎯 Exam Tip: Clearly define each of the three major stages (evapotranspiration, precipitation, runoff) and briefly explain what happens in each, mentioning their importance in the cycle.

Question 2. Distinguish between evaporation and transpiration.
Answer: Water boils at 100°C (212°F) but actually begins to evaporate at 0°C (32°F). Much of the water plants take up is released through transpiration.

🎯 Exam Tip: When distinguishing, provide clear, contrasting points for each term, focusing on their mechanisms and specific contexts.

Question 3. Give a detailed explanation on different forms of precipitation.
Answer: The form of precipitation depends on the weather and climate of a region.
• **Rain:** This is the most common type of precipitation. It consists of water droplets. Rain occurs when water droplets in clouds become heavy enough to fall.
• **Drizzle:** Drizzle consists of very small rain droplets, less than 0.5 mm in diameter. It is a light form of precipitation often found in warmer regions.
• **Snow:** In colder regions, precipitation can fall as snow or ice. Snow is formed when water vapor in the atmosphere freezes directly into ice crystals.
• **Sleet:** Sleet is a mix of water droplets and tiny ice particles. It forms when raindrops fall through a layer of freezing air near the ground.
• **Freezing Rain:** This happens when raindrops fall through cold air but don't freeze in the air. Instead, they freeze only when they hit a cold surface on the ground, creating a layer of ice.
• **Hail:** Hail consists of round pellets of ice, usually larger than 5mm in diameter. Hailstones form inside strong thunderstorms where updrafts and downdrafts carry water droplets up and down through freezing layers.
In simple words: Precipitation is water falling from clouds in different forms like rain, snow, sleet, freezing rain, and hail. Each form depends on the temperature and weather conditions in the air.

🎯 Exam Tip: For each form of precipitation, explain its basic composition (water, ice, or mixed) and the conditions under which it forms.

Question 4. Explain the run-off and its types.
Answer: Runoff is water pulled by gravity that moves across the land's surface. It helps refill groundwater and surface water by soaking into an aquifer (an underground water-bearing rock layer) or flowing into a river, stream, or watershed. Runoff comes from rain, melted snow, irrigation, or other sources when the ground cannot absorb all the water. It also causes erosion, forming canyons and other landforms.
**Types of Runoff:** Based on how quickly runoff occurs after rainfall, it can be classified into three types:
1. **Surface Runoff:** This is the portion of rainfall that enters a stream right after the rain. It happens when rainfall is long, heavy, and faster than the ground can soak it up (infiltration). The excess water then flows over the ground as "overland flow" and eventually joins streams, channels, or oceans.
2. **Sub-Surface Runoff (Interflow):** This is water that has seeped into the topsoil and moves sideways through the ground without reaching the deep groundwater table. It eventually flows into streams, rivers, or oceans. Sub-surface runoff is often called interflow.
3. **Base Flow:** This is the flow of underground water from a saturated groundwater zone into a water channel. It usually appears downstream where the channel elevation is lower than the groundwater table. Groundwater provides a steady flow to streams during dry periods when there is little or no precipitation.
In simple words: Runoff is all the water that flows over or under the ground into rivers and oceans. There are three types: surface runoff (flows on top), sub-surface runoff (flows just under the surface), and base flow (comes from deep underground water).

🎯 Exam Tip: Define runoff and then clearly differentiate its three types based on their flow paths and sources, explaining when each type typically occurs.

Samacheer Kalvi 8th Social Science Hydrologic Cycle Additional Important Questions and Answers

I. Choose the Correct answer.

Question 1. The process of change of water into gaseous form is called
a) Evaporation
b) Evapotranspiration
c) Precipitation
d) Condensation
Answer: (a) Evaporation
In simple words: When water turns from liquid into a gas, like water turning into steam from a hot pot, it's called evaporation.

🎯 Exam Tip: Remember that evaporation is the specific process of liquid changing to gas, a core component of the water cycle.

Question 2. ............... is the prime element which affects the rate of evaporation.
a) Temperature
b) Rain
c) Air
d) Mist
Answer: (a) Temperature
In simple words: Heat, or temperature, is the most important thing that makes water evaporate faster. The warmer it is, the quicker water turns into vapor.

🎯 Exam Tip: Higher temperatures provide more energy for water molecules to escape into the air, thus increasing the rate of evaporation.

Question 3. The quantity of water present on the earth is about ................ million cubic miles.
a) 236
b) 263
c) 326
d) 362
Answer: (c) 326
In simple words: Earth holds a huge amount of water, about 326 million cubic miles in total. This includes all the water in oceans, lakes, rivers, and underground.

🎯 Exam Tip: While specific numbers can be hard to recall, understanding the vast scale of water on Earth is important for comprehending the hydrologic cycle.

Question 4. ................ Saturation occurs when the temperature drops down.
a) Air
b) Water
c) Land
d) Soil
Answer: (a) Air
In simple words: Air becomes saturated when it gets colder, meaning it can no longer hold all the water vapor it contains. This leads to condensation.

🎯 Exam Tip: Air saturation is critical for understanding condensation and cloud formation; colder air holds less moisture.

Question 5. ............... of the moisture form plants through transpiration.
a) 10%
b) 50%
c) 80%
d) 90%
Answer: (a) 10%
In simple words: About 10% of the moisture in the atmosphere comes from plants releasing water vapor. This process is called transpiration.

🎯 Exam Tip: Recognize the significant, though smaller, contribution of transpiration from plants to atmospheric moisture compared to direct evaporation from water bodies.

Question 6. The evaporation is more than precipitation in the ................
a) Oceans
b) Land side
c) Desert land
d) Water Source
Answer: (a) Oceans
In simple words: More water evaporates from the oceans than falls back into them as rain. This extra water vapor then moves over land and falls as precipitation there.

🎯 Exam Tip: The oceans are the largest source of atmospheric moisture; evaporation from oceans drives a large part of the global water cycle.

Question 7. The process of change of gaseous form of water into liquid form is called as
a) Vapourisation
b) Transpiration
c) Condensation
d) Infiltration
Answer: (c) Condensation
In simple words: When water vapor, which is a gas, changes back into liquid water, it's called condensation. This is how clouds are formed.

🎯 Exam Tip: This question tests a fundamental definition in the water cycle; clearly distinguish condensation from other processes like vaporization or infiltration.

Question 8. An air layer next to the earth's Surface to 1000 m or lower is called as
a) Dew
b) Frost
c) Fog
d) Mist
Answer: (c) Fog
In simple words: Fog is like a cloud that forms very close to the ground, usually within 1000 meters of the Earth's surface. It makes it hard to see.

🎯 Exam Tip: Understand that fog is essentially a cloud at ground level, formed by condensation in the lowest part of the atmosphere.

Question 9. Water entering the soil at the Surface of the ground is termed as
a) Infiltration
b) Percolation
c) Condensation
d) Vaporisation
Answer: (a) Infiltration
In simple words: When water soaks into the ground from the surface, it is called infiltration. It's the first step for water to become groundwater.

🎯 Exam Tip: Differentiate infiltration (entering the soil) from percolation (moving through the soil layers deeper down).

Question 10. The flow of water from the unsaturated zone to the Saturated zone is termed as
a) Infiltration
b) Percolation
c) Condensation
d) Vaporisation
Answer: (b) Percolation
In simple words: After water infiltrates the soil, it then moves downwards through the soil layers from areas that are not fully wet (unsaturated) to areas that are completely wet (saturated). This downward movement is percolation.

🎯 Exam Tip: Percolation describes the deeper, downward movement of water through the soil and rock, replenishing groundwater.

II. Fill in the blanks:

Question 1. Water in India is available in Three Sources.
Answer: Water in India is available in three sources.
In simple words: India gets its water from three main places: rain and snow, water in rivers and lakes, and water stored underground.

🎯 Exam Tip: When listing sources of water for a specific region, consider both atmospheric (precipitation) and surface/sub-surface sources.

Question 2. Hydrology is the science which deals with the various aspects of water such as Occurrence, distribution, movement and properties on the planet earth.
Answer: Hydrology is the science which deals with the various aspects of water such as occurrence, distribution, movement and properties on the planet earth.
In simple words: Hydrology is the study of water on Earth. It looks at where water is found, how it spreads, how it moves, and what its features are.

🎯 Exam Tip: Emphasize that hydrology is the comprehensive scientific study of water, covering all its states and processes on Earth.

Question 3. Hydrologic cycle is a global Sun-driven process.
Answer: Hydrologic cycle is a global sun-driven process.
In simple words: The water cycle around the world is powered by the sun. The sun's energy makes water evaporate and move.

🎯 Exam Tip: Always remember that solar energy is the primary driving force behind the entire hydrologic cycle.

Question 4. Precipitation refers to all forms of water that fall from clouds and reaches the earth's Surface.
Answer: Precipitation refers to all forms of water that fall from clouds and reaches the earth's surface.
In simple words: Any water that falls from the sky to the ground, whether it's rain, snow, or hail, is called precipitation.

🎯 Exam Tip: Reiterate the broad definition of precipitation to include all forms of water falling from the atmosphere.

Question 5. The three important phases of the hydrologic cycle are Evapotranspiration, Precipitation, Run off.
Answer: The three important phases of the hydrologic cycle are Evapotranspiration, Precipitation, Run off.
In simple words: The three main stages of the water cycle are when water goes into the air (evapotranspiration), falls back down (precipitation), and then flows over land (runoff).

🎯 Exam Tip: Make sure to list the three key phases of the water cycle correctly, as these are fundamental to understanding the cycle.

Question 6. The Sleet falls, the raindrops freeze into solid particles of ice.
Answer: The Sleet falls, the raindrops freeze into solid particles of ice.
In simple words: When raindrops fall and freeze into small solid bits of ice before hitting the ground, it is called sleet.

🎯 Exam Tip: Differentiate sleet from freezing rain by noting that sleet freezes *in* the air, while freezing rain freezes *on* contact with surfaces.

Question 7. Most of the water on the earth is Saline in the surface water.
Answer: Most of the water on the earth is saline in the surface water.
In simple words: Most of the water we see on Earth's surface, like in oceans, is salty water.

🎯 Exam Tip: Reinforce the fact that the vast majority of Earth's surface water is saltwater, not freshwater.

Question 8. 2.15% is available in the form of glaciers.
Answer: 2.15% is available in the form of glaciers.
In simple words: A significant portion, about 2.15%, of the Earth's freshwater is stored in glaciers and icecaps.

🎯 Exam Tip: Understand that glaciers and icecaps represent a substantial reserve of freshwater, though not readily accessible.

Question 9. Hydrologic cycle is a continuous process and takes place naturally.
Answer: Hydrologic cycle is a continuous process and takes place naturally.
In simple words: The water cycle is always happening, never stops, and is a natural part of Earth's systems.

🎯 Exam Tip: Emphasize the constant and inherent nature of the water cycle as a natural phenomenon.

Question 10. Water boils at 100PC
Answer: Water boils at 100°C (Celsius).
In simple words: Water gets hot enough to boil and turn into steam at 100 degrees Celsius.

🎯 Exam Tip: Remember the standard boiling point of water in Celsius, which is 100°C.

Question 11. The water content in salt water oceans is 97.2%.
Answer: The water content in salt water oceans is 97.2%.
In simple words: Almost all the water on Earth, about 97.2%, is salty water found in the oceans.

🎯 Exam Tip: This figure highlights the dominance of oceans in global water distribution.

Question 12. The amount of Icecaps and glaciers in Fresh water is 68.7%.
Answer: The amount of Icecaps and glaciers in Fresh water is 68.7%.
In simple words: Out of all the freshwater on Earth, most of it, about 68.7%, is locked up in icecaps and glaciers.

🎯 Exam Tip: Understand that icecaps and glaciers are the largest reservoirs of freshwater on the planet.

Question 13. The Ground water content in Fresh water is 30.1%.
Answer: The Ground water content in Fresh water is 30.1%.
In simple words: After ice, the next biggest store of freshwater is underground water, which makes up about 30.1% of all freshwater.

🎯 Exam Tip: Recognize groundwater as the second-largest freshwater reservoir after glaciers and icecaps, and a crucial source for human use.

Question 6. The Sleet falls, the raindrops freeze into solid particles of ________.
Answer: The sleet falls when raindrops freeze into solid particles of ice. This happens when rain falls through a layer of air that is below the freezing point.
In simple words: When sleet falls, tiny drops of rain turn into solid pieces of ice.

🎯 Exam Tip: Remember that sleet is ice pellets, which are different from snow (ice crystals) and freezing rain (liquid that freezes on contact).

Question 7. Most of the water on the earth is ________ in the surface water.
Answer: Most of the water on the Earth's surface is saline. This means it contains a lot of salt, making it unsuitable for drinking or agriculture without treatment.
In simple words: Most of the water on Earth's surface has salt in it.

🎯 Exam Tip: Knowing the approximate percentage of saline versus freshwater helps understand global water scarcity.

Question 8. ________ is available in the form of glaciers.
Answer: Approximately 2.15% of the Earth's freshwater is available in the form of glaciers. These large ice masses store a significant portion of the planet's freshwater.
In simple words: A small part of Earth's water is stored as glaciers.

🎯 Exam Tip: Focus on understanding that glaciers are a major freshwater reserve, even if the overall percentage seems small.

Question 9. ________ is a continuous process and takes place naturally.
Answer: The hydrologic cycle is a continuous process and takes place naturally. This cycle constantly moves water above, on, and below the Earth's surface.
In simple words: The water cycle is a natural process that never stops.

🎯 Exam Tip: Understand that the hydrologic cycle is also known as the water cycle and is crucial for life on Earth.

Question 10. Water boils at ________.
Answer: Water boils at 100°C (100PC as in the source, assuming it means 100°C). At this temperature, water changes from a liquid to a gaseous state rapidly.
In simple words: Water gets very hot and turns into steam at 100 degrees Celsius.

🎯 Exam Tip: Remember the boiling point of water in Celsius, as it is a fundamental concept in science.

Question 11. The water content in salt water oceans is ________.
Answer: The water content in saltwater oceans is approximately 97.2%. This vast amount of saline water makes up the majority of Earth's total water.
In simple words: About 97.2% of all water is salty ocean water.

🎯 Exam Tip: Distinguish between the percentage of total water (mostly saline) and freshwater (a much smaller percentage).

Question 12. The amount of Icecaps and glaciers in Fresh water is ________.
Answer: The amount of icecaps and glaciers in freshwater is 68.7%. These frozen sources hold the largest share of the Earth's freshwater.
In simple words: Most of the fresh water on Earth is locked up in ice caps and glaciers.

🎯 Exam Tip: It is important to remember that icecaps and glaciers are the biggest reserves of freshwater, not groundwater or surface water.

Question 13. The Ground water content in Fresh water is ________.
Answer: The groundwater content in freshwater is 30.1%. This water is found beneath the Earth's surface in aquifers and is an important source for human use.
In simple words: A good portion of Earth's fresh water is found underground.

🎯 Exam Tip: Understand the relative proportions of freshwater sources: ice caps/glaciers are largest, followed by groundwater, and then surface water.

Question 14. The boiling point of water is ________.
Answer: The boiling point of water is 212°F. This temperature is equivalent to 100°C, a crucial point where water changes state.
In simple words: Water boils at 212 degrees Fahrenheit.

🎯 Exam Tip: Know the boiling point of water in both Celsius and Fahrenheit scales.

Question 15. There is a ________ relationship between temperature and evaporation.
Answer: There is a positive relationship between temperature and evaporation. This means as temperature increases, the rate of evaporation also increases because water molecules gain more energy.
In simple words: When it gets hotter, more water turns into vapor.

🎯 Exam Tip: Understand direct and inverse relationships in scientific concepts, like temperature and evaporation.

III. Match the following:
1. Runoff
2. Precipitation
3. Polar region
4. Infiltration
5. Drizzle
Answer:
1. Runoff - (e) river
2. Precipitation - (a) Rain
3. Polar region - (b) Snow
4. Infiltration - (c) Water springs
5. Drizzle - (d) less than 0.5mm
In simple words: Match each water term on the left with its correct description or related item on the right. Runoff flows into rivers, precipitation can be rain, polar regions have snow, infiltration recharges water springs, and drizzle has very small drops.

🎯 Exam Tip: When matching, eliminate the obvious pairs first and then focus on the trickier ones to increase accuracy.

IV. Choose the correct statement:

Question 1.
(a) Water entering the soil at the surface of the ground is termed as infiltration
(b) Rain water Soaks into the ground, through the soil and underlying rock layers.
(c) Some of the water remains underground and is called ground water.
(d) All of the options
Answer: (d) All of the options
In simple words: All the given statements about water moving into and through the ground are true. Infiltration is water entering the soil, rainwater soaking in is part of this, and groundwater is the water that stays underground. Infiltration and percolation are often used to mean similar things about water movement into and through soil.

🎯 Exam Tip: For "All of the options" choices, quickly verify if each individual statement is plausible and correct before selecting the final answer.

V. State whether the following statements are True or False:

Question 1. Water in India is available in three sources.
Answer: True. Water in India is available from three main sources: precipitation (rain), surface water (rivers, lakes), and groundwater (underground reservoirs). Understanding these sources helps manage water resources effectively.
In simple words: Yes, India gets water from three types of places: rain, rivers/lakes, and underground water.

🎯 Exam Tip: Remember the three primary sources of water supply for any region: precipitation, surface water, and groundwater.

Question 2. Rain is the tiny droplets of water hanging in the air.
Answer: False. Rain consists of water droplets that are large enough to fall to the Earth's surface due to gravity. Tiny water droplets hanging in the air typically refer to mist, fog, or clouds.
In simple words: No, rain is water drops falling down, not just tiny drops floating in the air like mist.

🎯 Exam Tip: Differentiate between various forms of atmospheric water like rain, mist, fog, and clouds based on droplet size and behavior.

Question 3. Saturation occurs when the temperature increases.
Answer: False. Saturation, especially referring to air holding water vapor, typically occurs when the temperature decreases. Colder air can hold less moisture, so when air cools, it reaches its saturation point more easily, leading to condensation. This is why dew forms on cold mornings.
In simple words: No, saturation happens when the air gets colder, not warmer. Cold air cannot hold as much water vapor.

🎯 Exam Tip: Understand the inverse relationship between air temperature and its capacity to hold water vapor for concepts like condensation and dew point.

Question 4. Evaporation is the process in which the liquid form of water changes into a gaseous form.
Answer: True. Evaporation is indeed the process where liquid water turns into water vapor (gaseous form), usually due to heat energy. This is a key part of the water cycle.
In simple words: Yes, evaporation is when liquid water turns into a gas.

🎯 Exam Tip: Clearly distinguish between evaporation (liquid to gas) and condensation (gas to liquid), which are opposite processes.

VI. Answer in brief:

Question 1. What are the Sources of water available in India.
Answer: The primary sources of water available in India are:
• Precipitation: This includes rainfall and snowfall.
• Surface water: This refers to water found in rivers, lakes, ponds, and reservoirs.
• Groundwater: This is water stored beneath the Earth's surface in aquifers. These three sources together fulfill the country's water needs.
In simple words: India gets its water from rain and snow, from rivers and lakes, and from underground water.

🎯 Exam Tip: When listing sources, always provide distinct categories like precipitation, surface water, and groundwater for a comprehensive answer.

Question 2. What is hydrology?
Answer: Hydrology is the scientific study of water on Earth. It specifically deals with the occurrence, distribution, movement, and properties of water on our planet. This field helps us understand how water moves through the environment and interacts with it.
In simple words: Hydrology is the study of water, where it is found, how it moves, and what it is like on Earth.

🎯 Exam Tip: Define key scientific terms precisely and include the main aspects of their study for full marks.

Question 3. What are the factors that increase the rate of evaporation?
Answer: The factors that increase the rate of evaporation are:
• Increase in wind speed: Wind carries away water vapor, allowing more liquid water to evaporate.
• Increase in temperature: Higher temperatures provide more energy for water molecules to escape into the air.
• Decrease in humidity: Dry air can absorb more water vapor than humid air.
• Increase in the areal extent of surface water bodies: A larger exposed water surface allows more water to evaporate. These factors all contribute to quicker drying.
In simple words: Stronger wind, hotter weather, drier air, and bigger water surfaces all make water evaporate faster.

🎯 Exam Tip: Listing factors with a brief explanation for each shows a deeper understanding of the concept.

VII. Give reasons:

Question 1. Availability of water on the earth is not uniform. Why?
Answer: The availability of water on Earth is not uniform because water resources are distributed unevenly across the globe. Some regions, like coastal areas or those with heavy rainfall, have abundant water, while others, such as deserts or drought-prone areas, have very limited access. This difference is due to climate patterns, geographical features, and human activities.
In simple words: Water is not found in the same amount everywhere on Earth because some places get more rain or have more rivers than others.

🎯 Exam Tip: When explaining uneven distribution, mention both natural factors (climate, geography) and human impacts if applicable.

Question 2. Distinguish between Frost and Mist.
Answer:

🎯 Exam Tip: For distinctions, always present clear, contrasting points for each item, ideally in a table format for clarity.

VIII. Answer in a paragraph:

Question 1. Water on the Earth – Explain.
Answer: About 71% of the Earth's surface is covered by water. The total amount of water on Earth is approximately 326 million cubic miles, which is a massive quantity. Most of this water, about 97.2%, is saline (salty) and found in oceans and seas, making it unsuitable for direct consumption. Only about 2.8% of the Earth's water is freshwater. Of this freshwater, about 2.2% is surface water, while the remaining 0.6% is groundwater. A large part of this surface freshwater, 2.15%, is stored in glaciers and icecaps. A smaller portion, 0.01%, is in lakes and streams, and 0.04% is in other forms. From the total groundwater, only about 0.25% can be easily taken out using current drilling methods. This shows how little freshwater is actually accessible for human use.
In simple words: Earth is mostly covered by water, but most of it is salty ocean water. Only a small part is fresh, and even less of that fresh water is easy for us to use, as much is frozen in ice or deep underground.

🎯 Exam Tip: Provide specific percentages when explaining water distribution, as they are key details to demonstrate knowledge.

Question 2. Explain the forms of condensation.
Answer: Condensation occurs when water vapor in the air changes back into liquid water or ice. The main forms of condensation include:
• Dew: These are water droplets that form when water vapor condenses on a relatively cold surface of an object, like grass, whose temperature drops below the dew point.
• Frost: These are ice crystals that form when water vapor directly turns into ice on a cold surface, typically when the temperature is below freezing.
• Fog: This is a cloud that forms near the Earth's surface. It consists of tiny water droplets or ice crystals suspended in the air, reducing visibility.
• Mist: Similar to fog, mist also consists of tiny water droplets hanging in the air but is less dense than fog, allowing for better visibility.
• Clouds: These are visible masses of tiny water droplets or ice particles suspended in the atmosphere, formed when water vapor condenses around small dust particles high above the Earth. Each form is a way for water vapor to become visible liquid or solid water.
In simple words: Condensation happens when water vapor in the air turns back into liquid or ice. The different types are dew (water drops on surfaces), frost (ice on surfaces), fog (thick cloud near the ground), mist (light fog), and clouds (water drops high in the sky).

🎯 Exam Tip: When explaining forms of condensation, clearly state how each form differs in appearance, location, and conditions of formation.