How to Use This Page
Attempt each question on your own before checking the solutions below. Understanding the process behind each answer matters more than memorising it. Use the Key Concepts table for quick revision and the Exam Checklist to verify your preparation.
Key Concepts (Quick Recap)
| Term | Definition |
|---|---|
| Hydrologic cycle | Global sun-driven process moving water between oceans, atmosphere, and land |
| Evaporation | Process of liquid water changing into gaseous form (water vapour) |
| Condensation | Process of water vapour changing back into liquid form |
| Transpiration | Release of water vapour from plant leaves into the atmosphere |
| Evapotranspiration | Total water loss from Earth's surface through evaporation and transpiration combined |
| Precipitation | All forms of water falling from clouds to Earth's surface (rain, snow, sleet, hail, drizzle) |
| Runoff | Water pulled by gravity across the land surface into streams, rivers, and oceans |
| Infiltration | Water entering the soil at the surface |
| Percolation | Water moving through soil and rock layers to reach groundwater |
| Aquifer | Underground layer of water-bearing rock or sediment that stores and transmits groundwater |
| Potable water | Water that is safe and suitable for human consumption (drinking) |
| Isohyet | Imaginary line joining places with equal rainfall |
| Drizzle | Precipitation with raindrop size less than 0.5 mm in diameter |
| Surface runoff | Portion of rainfall that enters streams immediately after rainfall |
| Sub-surface runoff (Interflow) | Water that enters the subsoil and moves laterally to streams without joining the water table |
| Base flow | Flow of underground water from a saturated groundwater zone to a water channel |
| Lapse rate | Not applicable to hydrologic cycle but temperature decreases 6.5°C per 1000 m altitude |
I. Choose the Correct Answer (MCQs)
1. The process in which water moves between oceans, atmosphere and land is called:
- a) River Cycle b) Hydrologic Cycle c) Rock Cycle d) Life Cycle
The hydrologic cycle describes the continuous movement of water between oceans, atmosphere, and land.
2. The percentage of fresh water on the earth is:
- a) 71 b) 97 c) 2.8 d) 0.6
Only 2.8% of Earth's total water is fresh water; 97.2% is saline.
3. The process of changing water from gaseous to liquid form is known as:
- a) Condensation b) Evaporation c) Sublimation d) Rainfall
Condensation converts water vapour (gas) back into liquid form, forming clouds and dew.
4. Water that flows in the sub-soil or through the ground into streams, rivers, lakes and oceans is termed as:
- a) Condensation b) Evaporation c) Transpiration d) Runoff
Runoff is water that flows over or through the ground into water bodies.
5. The evaporation of water from the leaves of plants is called:
- a) Transpiration b) Condensation c) Water vapour d) Precipitation
Transpiration is the release of water vapour from plant leaves into the atmosphere.
6. Water that is good enough to drink is called:
- a) Groundwater b) Surface water c) Potable water d) Artesian water
Potable water is safe and suitable for human consumption.
7. Process of change of water into gaseous form is called:
- a) Evaporation b) Evapotranspiration c) Precipitation d) Condensation
Evaporation is the process of liquid water changing into water vapour (gas).
8. ______ is the prime element affecting evaporation rate.
- a) Temperature b) Rain c) Air d) Mist
9. Quantity of water on earth is about ______ million cubic miles.
- a) 236 b) 263 c) 326 d) 362
10. Change of gaseous water into liquid form is called:
- a) Vapourisation b) Transpiration c) Condensation d) Infiltration
11. An air layer next to earth's surface to 1000m or lower is called:
- a) Dew b) Frost c) Fog d) Mist
Fog is a layer of suspended tiny water droplets near the Earth's surface up to about 1000m.
12. Water entering the soil at the surface is termed as:
- a) Infiltration b) Percolation c) Condensation d) Vaporisation
13. Flow of water from unsaturated zone to saturated zone is termed as:
- a) Infiltration b) Percolation c) Condensation d) Vaporisation
II. Fill in the Blanks
1. The degree of water vapour present in the atmosphere is known as weather. 2. There are Three phases in the water cycle. 3. The falling of water towards the earth surface from the atmosphere in any form is known as Precipitation. 4. The precipitation with a rain drop size of <0.5mm in diameter is known as drizzle. 5. Mist is denser than Clouds. 6. Water in India is available in three sources. 7. Hydrology deals with aspects of water such as occurrence, distribution, and movement. 8. Hydrologic cycle is a global sun-driven process. 9. Precipitation refers to all forms of water falling from clouds to earth's surface. 10. Three important phases of the hydrologic cycle are Evapotranspiration, Precipitation, and Run off. 11. When sleet falls, raindrops freeze into solid particles of ice. 12. Most water on earth is saline in the surface water. 13. 2.15% of fresh water is available in the form of glaciers. 14. Ground water content in fresh water is 30.1%. 15. Boiling point of water is 212°F (or 100°C).
III. Match the Following
Textbook Match:
| No. | Column A | Answer |
|---|---|---|
| 1 | Vegetation | d) Transpiration |
| 2 | Condensations | a) Clouds |
| 3 | Snow and raindrops | b) Sleet |
| 4 | Infiltration | c) At the surface |
Additional Match:
| No. | Column A | 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 |
Third Match:
| No. | Column A | Answer |
|---|---|---|
| 1 | Evaporation | d) Liquid to gas |
| 2 | Condensation | a) Gas to liquid |
| 3 | Transpiration | b) Water from plants |
| 4 | Infiltration | c) Water enters soil surface |
| 5 | Percolation | e) Water moves through soil to groundwater |
IV. Choose the Correct Statement
Q1. Evaporation refers to — I. Gaseous form of water changes into liquid form. II. Liquid form of water changes into gaseous form. III. Water boils at 100°C but begins to evaporate at 0°C. IV. Responsible for formation of clouds.
- a) I, IV, V are correct b) II only correct c) II and III are correct d) All are correct
Statement II is correct (evaporation is liquid to gas). Statement III is also correct (water begins evaporating even at 0°C).
V. True or False
VI. Short Answer Questions
1. Short note on aquifer. An aquifer is an underground layer of water-bearing rock or sediment that stores and transmits groundwater. Wells are drilled into aquifers to extract water for drinking and irrigation. Aquifers are a vital source of fresh water, especially in areas where surface water is scarce. The water in aquifers moves slowly through permeable rock layers.
2. Define "hydrological cycle." The hydrological cycle is a global sun-driven process in which water is continuously transported from oceans to the atmosphere (through evaporation), from the atmosphere to the land (through precipitation), and from the land back to the oceans (through runoff). It is a closed system — the total amount of water on Earth remains constant, but water moves between different reservoirs.
3. How does dew formation take place? Dew forms when water vapour condenses on a relatively cold surface of an object. It occurs when the object's temperature drops below the dew point temperature, typically during clear, calm nights. The cold surface cools the air around it, causing water vapour to condense into tiny droplets. Dew is commonly seen on grass, leaves, and car windows in the early morning.
4. Short note on surface run-off. Surface runoff is the portion of rainfall that enters streams immediately after rainfall. It occurs when rainfall is longer, heavier, and exceeds the infiltration rate. The excess water moves across the ground surface (overland flow) and when it joins streams or oceans, it is called surface runoff. Surface runoff is a major contributor to soil erosion and can cause flooding in low-lying areas.
5. What are the sources of water available in India? Three main sources: precipitation (rainfall), surface water (rivers, lakes, ponds), and groundwater (wells, tube wells, springs). India receives most of its rainfall during the monsoon season (June-September). Major rivers like the Ganga, Yamuna, Godavari, Krishna, and Kaveri provide surface water, while groundwater is extracted through wells and tube wells for irrigation and drinking.
6. What is hydrology? Hydrology is the science dealing with aspects of water such as its occurrence, distribution, movement, and properties on Earth. It studies how water moves through the hydrologic cycle, including evaporation, precipitation, infiltration, percolation, and runoff. Hydrology helps in managing water resources, predicting floods, and planning irrigation and water supply systems.
VII. Give Reasons
1. Infiltration of water is low in the region of non-porous soil. Percolation moves infiltrated water through the soil profile and rock layers to form groundwater. Non-porous soil has very small or closed pores that impede this downward movement, resulting in low infiltration and more surface runoff. Sandy and loamy soils have higher infiltration rates than clayey or rocky soils.
2. Freshwater is less on the earth. Most water on Earth is saline, found in seas and oceans, constituting about 97.2%. Only 2.8% is fresh water, and of that, about 68.7% is locked in icecaps and glaciers, and 30.1% is groundwater. Only about 0.25% of total groundwater can be economically extracted. This makes available fresh water a very small fraction of Earth's total water.
3. Snowfall is common in the polar region and mountainous regions. Water vapour in clouds is converted directly into snow pieces due to extremely low temperatures, which is common in polar and high mountainous regions where temperatures remain below freezing. The cold conditions cause water vapour to deposit as ice crystals rather than forming raindrops.
4. Evaporation starts even at 0°C, not just at boiling point. Water does not need to reach its boiling point (100°C or 212°F) to evaporate. Evaporation occurs at all temperatures, including 0°C, because individual water molecules at the surface gain enough energy from ambient heat to escape into the atmosphere. Boiling is rapid evaporation throughout the liquid, but surface evaporation happens continuously at any temperature.
VIII. Detailed Answer Questions
Common Mistakes
1. ❌ Confusing evaporation and transpiration: Evaporation is from surface water; transpiration is from plant leaves. ✅ Evaporation = surface water to gas; Transpiration = plants release water vapour. 2. ❌ Mixing infiltration and percolation: Infiltration = water entering soil at surface; percolation = water moving through soil layers to groundwater. ✅ Infiltration = enters surface; Percolation = moves downward. 3. ❌ Confusing sub-surface runoff and base flow: Sub-surface runoff (interflow) moves laterally through subsoil; base flow comes from saturated groundwater zones. ✅ Interflow = lateral; Base flow = upward from water table. 4. ❌ Assuming all fresh water is usable: 68.7% is in icecaps/glaciers; only about 0.25% of groundwater can be economically extracted. ✅ Available fresh water is very limited. 5. ❌ Confusing drizzle and rain: Drizzle drops are < 0.5mm; rain drops are > 0.5mm. ✅ Drizzle = tiny drops; Rain = bigger drops. 6. ❌ Mixing fog and mist: Fog is denser and reduces visibility more; mist has larger droplets than fog but is less dense than clouds. ✅ Fog = dense, low visibility; Mist = less dense than fog. 7. ❌ Forgetting that water evaporates at 0°C: Water doesn't need to boil (100°C) to evaporate; evaporation starts at 0°C. ✅ Evaporation occurs at ALL temperatures above 0°C.
Exam Checklist
- [ ] Can define the hydrologic cycle and name its three phases
- [ ] Know the distribution of water on Earth (97.2% saline, 2.8% fresh)
- [ ] Can distinguish evaporation, transpiration, and evapotranspiration
- [ ] Can list and describe all forms of precipitation (rain, drizzle, sleet, freezing rain, hail, snow)
- [ ] Can explain the three types of runoff (surface, sub-surface, base flow)
- [ ] Understand infiltration vs. percolation clearly
- [ ] Can define aquifer, potable water, dew, frost, fog, and mist
- [ ] Know the forms of condensation and their differences
- [ ] Remember that water evaporates at 0°C (not just at boiling point)
- [ ] Can explain why fresh water is scarce on Earth (97.2% saline, 68.7% of fresh water in glaciers)
- [ ] Know the difference between surface runoff, interflow, and base flow
- [ ] Can give reasons for low infiltration in non-porous soil and snowfall in polar regions
Internal Links
- [Class 8 Social Science Guide](/class/8/social)
- [Hydrologic Cycle — Chapter Guide](/class/8/social/hydrologic-cycle)
- [Weather and Climate — Exercise Solutions](/class/8/social/solutions/weather-and-climate-exercise-solutions)
- [Rocks and Soils — Exercise Solutions](/class/8/social/solutions/rocks-and-soils-exercise-solutions)