A Journey through States of Water Class 6 Question Answer Science Chapter 8

A Journey through States of Water Class 6 Questions and Answers NCERT Solutions

Class 6 Science Chapter 8 A Journey through States of Water Question Answer

A Journey through States of Water Class 6 Intext Questions

Page – 154

Question 1.
Reflect on what you did really well in activity 8.7 ?
Answer:

• Accurate measurement: I ensured that the amount of water used in each condition was same, which gave the accurate results.
• Careful observation: I closely monitored the evaporation process, noting the time taken for water to evaporate under different conditions. This attention to detail was crucial for drawing valid conclusions.
• Understanding variables: I effectively identified and controlled the variables in the experiment, such as temperature, air movement and humidity. This allowed me to isolate the effects of each factor on the rate of evaporation.
• Data recording: I kept thorough and organised records in Table 8.5, which helped me compare the effects of different conditions clearly.
• Drawing conclusions: I was able to accurately interpret the results and understand how each factor contributed to the evaporation process, deepening my understanding of the concept.

Page – 159

Question 1.
In activity 8.11 , What did I do well? Was I able to label all the parts of the water cycle? Which parts of the water cycle were unclear to me?
Answer:
(i) I was able to correctly identify and label the main stages of the water cycle, including evaporation, condensation, precipitation and collection. I also understood how water changes state between liquid, gas and solid during these processes.

(ii) Yes, I labelled all the main parts of the water cycle correctly.

(iii) I found the process of condensation a bit confusing, especially how water vapour in the air turns into tiny droplets to form clouds. I also wasn’t completely sure about the role of dust particles in cloud formation and how that leads to precipitation. These are areas I would like to understand better.

A Journey through States of Water Class 6 Textbook Questions

Question 1.
Which of the following best describes condensation?
(a) The conversion of water into its vapour state.
(b) The process of water changing from a liquid into the gaseous state.
(c) The formation of clouds from tiny water droplets.
(d) The conversion of water vapour into its liquid state.
Answer:
(d) The conversion of water vapour into its liquid state.
Explanation: Condensation is the process where water vapour in the air cools down and changes back into liquid water, forming droplets.

Question 2.
Identify in which of the given processes, evaporation is very important-
(Medium)
(i) Colouring with
(a) crayons
(b) water colours
(c) acrylic colours
(d) pencil colours
Answer:
(b) water colours
Explanation: evaporation is important to dry the colours on paper.

(ii) Writing on paper with
(a) pencil
(b) ink pen
(c) ballpoint pen
Answer:
(b) ink pen
Explanation: Evaporation is crucial in ink pens as the solvent in the ink evaporates, leaving behind the solid pigment on the paper.

Question 3.
We see green-coloured plastic grass in many places these days. Space around natural grass feels cooler than space around plastic grass. Can you find out why?
Answer:
Natural grass absorbs and evaporates water through its surface, which helps in cooling the surrounding area. Plastic grass does not have this property; it cannot absorb and evaporate water, so it does not cool its surroundings. As a result, the space around natural grass feels cooler compared to plastic grass.

Question 4.
Give examples of liquids other than water, which evaporate.
Answer:
Examples of liquids that evaporate other than water include:

• Alcohol (e.g., ethanol)
• Acetone
• Gasoline
• Perfumes

Question 5.
Fans move air around, creating a cooling sensation, It might seem strange to use a fan to dry wet clothes since fans usually make things cooler, not warmer. Normally, when water evaporates, it requires heat, not cold air. What do you think about this?
Answer:
Fans do not cool the air but move it around, which helps to increase the rate of evaporation. When a fan blows air over wet clothes, it removes the humid air near the surface of the clothes and speeds up the evaporation process, thus drying the clothes more quickly. The cooling sensation is due to the increased rate of evaporation from the skin.

Question 6.
Usually, when sludge is removed from drains, it is left in heaps next to the drain for 3-4 days. Afterwards, it is transported to a garden or a field where it can be used as manure. This approach reduces the transportation cost of the sludge and enhances the safety of individuals handling it. Reflect upon it and explain how.
Answer:
Leaving the sludge in heaps allows it to dehydrate due to evaporation, reducing its volume and weight. This makes it cheaper and easier to transport. Additionally, the drying process makes the sludge less messy and safer to handle, improving hygiene and safety during transportation.

Question 7.
Observe the activities in your house for a day. Identify the activities that involve evaporation. How does understanding the process of evaporation help us in our daily activities?
Answer:
Activities involving evaporation at home include:

• Drying clothes on a clothesline.
• Using a fan to speed up the drying of wet surfaces.
• Cooking food, where water evaporates from boiling or simmering liquids.

Understanding evaporation helps us manage resources more efficiently, such as improving drying processes, reducing energy consumption and ensuring proper use of water.

Question 8.
How is water present in the solid state of nature?
Answer:
Water is present in a solid state in nature, like ice. This includes glaciers, ice caps, snow and frost. These forms of ice are found in cold environments, such as polar regions and high mountain ranges.

Question 9.
Reflect on the statement, “Water is our responsibility before it is our right.” Share your thoughts.
Answer:
This statement emphasises the importance of conserving and protecting water resources. It highlights that while we have the right to access clean water, it is also our responsibility to use it wisely and sustainably. By being mindful of our water usage, we can ensure that this vital resource is available for future generations and prevent water scarcity.

Question 10.
The seat of a two-wheeler parked on a sunny day has become very hot. How can you cool it down?
Answer:
To cool down a hot seat on a two-wheeler, you can:

• Place a wet cloth or towel over the seat to help absorb heat through evaporation.
• Use a fan to blow air over the seat, which will increase the rate of cooling.
• Move the vehicle to a shaded area to prevent further heating.

A Journey through States of Water Class 6 NCERT Exemplar Questions

Multiple Choice Questions

Question 1.
Which of the following activities does not involve the use of water?
(a) Washing clothes
(b) Bathing
(c) Cleaning utensils
(d) Drying wet clothes
Answer:
(d) Drying wet clothes
Explanation: Washing, bathing and cleaning utensils are activities which require the use of water, whereas in drying wet clothes, water gets converted into vapour form.

Question 2.
In which of the following activities will you use the minimum amount of water?
(a) Bathing
(b) Brushing teeth
(c) Washing clothes
(d) Mopping a room
Answer:
(b) Brushing teeth
Explanation: Bathing, washing clothes and mopping a room will require a large amount of water. The minimum amount of water will be required for brushing teeth.

Question 3.
Water in our tap comes from a
(a) river
(b) lake
(c) well
(d) river, lake or well.
Answer:
(d) river, lake or well.
Explaniation: Water in our tap comes from rivers, lakes or wells. Before supplying the water through a tap, it is routed through water treatment plants. The water drawn from these sources is fit for consumption.

Question 4.
In which of the following case evaporation of water will be slowest?
(a) A tray of water kept in sunlight.
(b) A kettle of water kept on a burner.
(c) A glass of water kept in a room.
(d) A bucket of water kept on the rooftop.
Answer:
(c) A glass of water kept in a room.
Explanation: Evaporation is affected by temperature. When temperature increases, evaporation also increases. Room temperature is the lowest temperature compared to sunlight, the burner, and the rooftop. So, a glass of water kept in a room has the slowest water evaporation.

Question 5.
Clouds are
(a) tiny drops of water floating in the air
(b) mixture of dust and water vapour.
(c) particles of water vapour.
(d) raindrops in the air.
Answer:
(a) tiny drops of water floating in the air
Explanation: At sufficient heights, water vapour present in the air condenses to form tiny droplets of water floating in the air, which appear to us as clouds. Later, these tiny water droplets come together to form larger-sized water drops and become so heavy that they begin to fall in the form of rain.

Very Short Answer Type Questions

Look at figure.

Question 6.
Write down activities shown in this figure in which water is being used.
Answer:
The activities shown in the given figure in which water is being used are :
(i) Bathing
(ii) Washing clothes.

Question 7.
Write any two activities which require more than a bucket of water.
Answer:
The two activities which require more than a bucket of water are:
(i) washing ten clothes or more.
(ii) irrigating a crop field.

Question 8.
Write any two activities which require less than one bucket of water.
Answer:
The two activities which require less than one bucket of water are :
(i) brushing teeth
(ii) wasking a handkerchief.

Short Answer Type Questions

Question 9.
Why do wet clothes placed on a clothesline get dry after some time?
Answer:
On exposure to heat, water present in wet clothes gets converted into water vapour due to evaporation, and as a result, clothes get dry after some time.

Question 10.
Water kept in sunlight gets heat from the sun and is evaporated. But how does water kept under the shade of a tree also get evaporated? Explain.
Answer:
Air around us gets heated from sunlight. This warm air provides heat for evaporation of water kept under the shade of a tree.

Question 11.
Why is there a need for conserving water? Give two reasons.
Answer:
There is a need for conserving water because:
(i) The demand for water is increasing day-by-day, with the rise in population, but the amount of water available for use is very limited.
(ii) The level of groundwater is decreasing drastically, which would lead to extreme water scarcity in the near future.

Question 12.
Fill in the blanks by selecting words from the following list.
snow, rain, clouds, vapour, evaporation, transpiration. Water, as ________ goes into atmosphere by the processes of ________ and ________ and forms ________ ,which on condensation falls in the form of ________ and ________ .
Answer:
vapour, evaporation, transpiration, clouds, snow, rain

Long Answer Type Questions

Question 13.
Most of the water that falls on the land as rain and snow sooner or later goes back to the sea or an ocean. Explain how it happens.
Answer:
Most of the water that falls on land as rain and snow eventually returns to the sea or ocean through a series of processes in the water cycle:
(i) Precipitation: Water falls from the atmosphere to the Earth’s surface in the form of rain, snow, sleet or hail.
(ii) Runoff: After precipitation, some of the water flows over the ground in streams and rivers. This surface runoff gathers and travels towards larger bodies of water, such as lakes, rivers and eventually the seas or oceans.
(iii) Infiltration and Percolation: Water that does not flow over the surface can infiltrate into the soil. It then percolates down through the soil layers to replenish groundwater reserves. This groundwater eventually finds its way to rivers, lakes and seas.
(iv) Evaporation: Water from the surface of oceans, seas and other bodies of water evaporates into the atmosphere due to heat from the sun. This water vapour rises into the atmosphere.
(v) Transpiration: Plants absorb water from the soil through their roots and release it into the atmosphere through their leaves in a process called transpiration. This adds to the atmospheric water vapour.
(vi) Condensation: Water vapour in the atmosphere cools and condenses to form clouds. This process eventually leads to precipitation.
(vii) Collection: Precipitation collects in various bodies of water, such as rivers, lakes and oceAnswer: Rivers eventually flow into seas or oceans, where the cycle starts again.

Question 14.
Dissolve two spoons of common salt in half a cup of water. Now if you want to get the salt back, what will you do?
Answer:
To get the salt back after dissolving it in water, you can use the process of evaporation. Here’s how you can do it:
(i) Evaporation: Pour the saltwater solution into a shallow dish or pan. Place the dish in a warm, dry area or use a heat source like a stove or a hot plate to speed up the evaporation process. As the water evaporates, the salt will start to crystallise and be left behind in the dish.
(ii) Crystallisation: Once all the water has evaporated, you will be left with the salt crystals. You can scrape or collect the crystals to retrieve the salt.

Introduction :

Introduction to Water States

Comparing Ice and Water
Thirav’s View:

• Observation: Ice and water are different substance because they have different physical properties.
• Ice characteristics: Solid, hard, retains shape.
• Water characteristics: Liquid, flows, takes the shape of the container.

Aavi’s View:

• Observation: Ice and water are the same substance in different states.
• Explanation: Ice melts into water and water freezes into ice, demonstrating they are the same substance.
• Thirav’s doubt about whether something gets added to the ice in the freezer is a misunderstanding of the process.
• In reality, ice and water are the same substance in different states.

Explanation:

• Ice and Water relationship: Ice is simply the solid form of water. Water freezes and turns into ice at 0° C(32° F). The chemical composition remains the same: H₂O.
• Freezing process: When water is placed in a freezer, it loses heat and transition occurs from a liquid to a solid state. No new substances are added; rather, water just changes its state.

Activity 8.1 (Page-144)

Let us observe

Investigating Water’s Disappearing Act
On a rainy morning, Aavi and Thirav observed that water puddles in the playground had disappeared by the evening. This leads to questions about where the water goes. They wonder whether water disappears due to seepage or another reason. Aavi thinks that water might seep through the surface of utensils, while Thirav believes that water does not seep through.
Here are some questions related to this observation, followed by their answers:

Question 1.
Have you ever noticed water in the puddles disappearing? Where does it go?
Answer:
Yes, water in puddles disappears due to evaporation. In this process, water changes from a liquid to a gas and enters the atmosphere.

Question 2.
Where else have you seen water disappearing? Can you think of a possible reason why this happens?
Answer:
Water also disappears from surfaces like utensils after washing. The primary reason is evaporation, where heat from the surroundings causes the liquid water to turn into vapour and escape into the air.

Question 3.
You might have observed that after washing the utensils, water left on the surface of the utensils dries up after some time. Does the reason you thought earlier about explaining water disappearance apply in this case also?
Answer:
Yes, the reason for water disappearing from the surface of utensils is evaporation. The water turns into vapour due to heat and air exposure, not seepage.

Question 4.
Aavi wonders if water has seeped through the surface of the utensils. Thirav thinks that water does not seep through the surface of the utensils. Design an activity to investigate whose idea is correct.
Answer:
Activity:

1. Clean and dry different utensils (metal, plastic, ceramic).
2. Pour a specific amount of water into the utensils and mark the water level on each utensil. Observe them over a period of time.
3. After a set time, check the water level and dry the utensil’s surface.
4. Note any changes or signs of seepage.

Activity 8.2 (Page-114)

Let us investigate

Activity with Steel Plate:

Procedure:

1. Take a tablespoon of water and place it on a steel plate.
2. Observe whether the water seeps through other side of the plate or not.
3. Keep observing at regular intervals until the water completely disappears.

Inference:
If the water does not seep through the steel plate and completely disappears, it indicates that the water is not seeping through the steel plate. Instead, it is likely evaporating.

Conclusion:
This activity alone may not be enough to fully conclude that water does not seep through steel plates in all conditions. However, if the water disappears and no seepage is observed, evaporation is a likely cause.
Where has the Water gone? The water has converted into water vapour, a gaseous state, due to evaporation.
Sprinkling Water on a Hot Pan:

Observation:
When water is sprinkled on a hot pan, it disappears.

Explanation:
The water gets converted into steam (water vapour) when it comes in contact with the hot surface of the pan. vapour

Process: The conversion of water into its vapour state is called evaporation.

Examples of Evaporation:

• Drying of wet clothes: Water evaporates from the wet clothes into the air.
• Mopped floor: Water left on the floor evaporates over time.
• Sweat on our body: Sweat evaporates to cool down the body.

Reason for the Disappearance of Water from Puddles:

• Cause: The primary reason for the disappearance of water from puddles is evaporation. While some water may seep into the ground. Evaporation changes water into water vapour that goes into the atmosphere.

Disappearance of Hand Sanitiser:

• Observation: Hand sanitiser disappears when rubbed on hands.
• Explanation: The hand sanitiser contains alcohol, which evaporates quickly when rubbed to the skin. Alcohol is a volatile liquid that evaporates onexposed to air. As the alcohol evaporates, causing the sanitiser to disappear.

Activity 8.3 (Page-146)

Let us experiment

In this experiment, we will observe the process of condensation and explore the factors that influence it. We will start by placing ice cubes in a glass tumbler filled with cold water and then observe the changes that occur over time.

Below are possible reasons explaining the appearance of water droplets on the outer surface of the glass tumbler.

Dew drops on plants and water droplets on the inside of a steel plate after boiling water are both examples of condensation. Condensation occurs when water vapour turns into liquid water, usually due to a temperature change.

Question 1.
Why do we see dew drops more in the morning?
Answer:
Dew drops are more visible in the morning because the air cools down overnight. As the temperature drops, the air can no longer hold all its moisture, causing water vapour to condense into tiny droplets on the surfaces of plants.

Question 2.
When we boil water in a half-filled utensil and cover it with a steel plate, where do the water drop that accumulate on the inner side of the steel plate come from?
Answer:
The water drops on the inner side of the steel plate come from the steam (water vapour) rising from the boiling water. When the steam hits the cooler surface of the steel plate, it condenses back into liquid water, forming droplets on the plate.

Activity 8.4 (Page-148)

Let us measure

This experiment aims to investigate the process of condensation and measure the change in mass due to water vapour condensing on a cold surface. We will set up a glass tumbler with iee water, cover it ‘ weigh it on a digital balance. By recording the mass over time, we can observe the increase in mass caused by condensation.

Prediction: The mass of the water will increase over time. This is because we expect water vapour from the air to condense on the cold surface of the glass tumbler, adding to the total mass.

Observation table:

Time (min)	Mass of Water (g)
0	150
5	150.25
10	150.5
15	150.75
20	151
25	151.25
30	151.5

Question 1.
Does your findings match with your predictions? Explain your observations.
Answer:
Yes, our findings match with the predictions.
As predicted, the mass of the water in the glass tumbler increased over time. This increase is due to the condensation of water vapour from the air onto the cold surface of the glass. The water vapour, upon contact with the cold surface, changes its state from a gas to a liquid, adding to the total mass of the system.
Now repeat this activity with a modification. Mark the water level on the glass tumbler with a permanent marker or a visible tape.

Question 2.
What do you observe?
Answer:
Water level in the glass tumbler does not go down but the extra water gets collected on the outer surface of the glass tumbler.

Question 3.
What can you conclude from this?
Answer:
This activity shows that the water is not seeping from the glass tumbler and the extra water is being collected because of condensation.

Evaporation and Condensation

Process	Description	Example
Evaporation	Liquid water turns into vapour due to heat.	Puddle drying up on a sunny day.
Condensation	Water vapour turns into liquid water when cooled.	Dew on grass in the morning.

States of Water

State	Characteristics	Example Ice cube in a tray.
Solid	It retains shape and does not flow.	Water in a glass.
Liquid	Flows, takes the shape of the container.	Water vapour in the air.
Gas	Spreads out, no fixed shape.	Example Ice cube in a tray.

Activity 8.5 (Page-150)

Let us identify
This activity explores the properties of water in its three states: solid (ice), liquid (water) and gas (water vapour). By observing the behaviour of water in each state, we can understand the unique characteristics of each state and how they differ from one another.

By exploring examples of solids, liquids and gases in our surroundings, we can better understand how different materials behave under various conditions.

Question 1.
What are some examples of solid substances?
Answer:
Examples of solid substances include stones, wood, glass, metal and plastic.

Question 2.
What are other examples of liquids apart from milk and oil?
Answer:
Other examples of liquids include water, juice, vinegar, honey and shampoo.

Question 3.
Have you ever noticed that you could smell the food being cooked even without entering the kitchen? How does this smell reach us?
Answer:
The smell of food spreads through the air as tiny particles called odour molecules. These molecules travel through the air and reach our nostrils, allowing us to smell the food even if we are not in the kitchen.

Question 4.
What are other examples of gases you can think of?
Answer:
Other examples of gases include oxygen, carbon dioxide, helium, methane and nitrogen.

Changing States of Water

Water can exist in three states: solid (ice), liquid (water) and gas (water vapour). You can change the state of water by either heating or cooling it. This process is similar to other substances as well, such as wax or coconut oil.

Understanding how to change these states helps us grasp how matter behaves under different conditions.

Question 1.
How can you quickly change ice to its liquid state (water)?
Answer:
To quickly change ice into water, you need to supply heat. This can be done by placing the ice at room temperature or applying heat directly, such as using a stove or microwave.

Question 2.
How can you change water into ice?
Answer:
To change water into ice, you need to remove heat. This is done by placing the water in a cold environment, such as a freezer, where the temperature is low enough for the water to freeze into ice.

Question 3.
Can you think of any other example, besides water, that can change from solid to liquid?
Answer:
Yes, candle wax is another example. When heated, candle wax melts from a solid into a liquid.

Question 4.
How can we turn candle wax into a liquid state? How can we change the liquid wax back into a solid state?
Answer:
To turn candle wax into a liquid state, you need to heat it. To change the liquid wax back into a solid state, you need to cool it.

Question 5.
What other liquids have you seen that get converted into a solid?
Answer:
Other liquids that can convert into a solid include coconut oil, which can become solid during the winter season, and chocolate, which solidifies when cooled after melting.

Question 6.
Have you ever seen coconut oil getting converted into its solid state during the winter season?
Answer:
Yes, coconut oil can turn into a solid state during cooler temperatures or in the winter season.

• Melting: The process of a solid turning into a liquid (e.g., ice melting into water).
• Freezing: The process of a liquid turning into a solid (e.g., water freezing into ice).

Activity 8.6 (Page-152)

Let us complete the diagram using the words given in the box.

How can water be evaporated faster or slower?
Conditions Affecting Evaporation:

Condition	Effect on Evaporation	Explanation
Surface Area	Larger surface area speeds up evaporation.	More water is exposed to air.
Temperature	Higher temperature increases the rate.	Heat provides energy for water molecules to escape.
Wind	Wind accelerates evaporation.	Moves evaporated water away, exposing more water.
Humidity	Lower humidity speeds up evaporation.	Dry air allows more water to evaporate.

Question 1.
What are the conditions that affect how fast water evaporates?
Answer:
The conditions affecting the rate of evaporation include temperature, air movement (wind), humidity, surface area and exposure to sunlight.

Question 2.
What differences do you see in evaporation on a cold day versus a hot day?
Answer:
On a hot day, evaporation happens faster due to higher temperatures that provide more energy for water molecules to turn into vapour. On a cold day, evaporation occurs more slowly because lower temperatures provide less energy for the water molecules.

Activity 8.7 (Page-153)

Let us Investigate

Take water in a small cap of a bottle (you may use sanitiser in place of water). Take the same amount of water in a plate. The exposed area of water in the bottle cap and the plate are different.

Exposed area of water	Time taken for complete evaporation
Less (bottle cap)	15 minutes
More (plate)	30 minutes

Question 1.
What conditions did we keep the same?
Answer:
We kept the amount of water and the environment (e.g., temperature and air movement) the same for both the cap and the plate.

Question 2.
What did we change in this investigation?
Answer:
We changed the surface area exposed to air. The water in the bottle cap has a smaller surface area compared to the water spread out on the plate.

Question 3.
What did we measure?
Answer:
We measured the time taken for the water to evaporate completely from both the cap and the plate.

Question 4.
What can you conclude from this investigation?
Answer:
We can conclude that a larger exposed surface area leads to faster evaporation. The water in the plate, which had a larger surface area, evaporated faster than the water in the small cap.

Question 5.
What would happen if milk were taken instead of water in the above activity?
Answer:
If milk is used instead of water, the evaporation process may take longer. This is because milk contains proteins and fats in addition to water, which can affect the rate of evaporation. The presence of these additional substances can slow down the evaporation compared to pure water.

Other conditions which affect how fast water evaporates Designing an activity to explore other conditions affecting evaporation

Objective: To design an activity that explores how various conditions affect the rate at which water evaporates. We will investigate factors such as temperature, air movement, humidity and record the time taken for water to evaporate under different conditions.

Activity Setup:
1. Materials Needed:

• Three identical shallow plates
• Water
• Thermometer
• Fan or hairdryer (for air movement)
• Hygrometer (to measure humidity)
• Stopwatch or timer
• Measuring cup

2. Steps:
(i) Label the three plates as A, B and C. Pour an equal amount of water into each plate with the help of measuring cup (e.g. 50 ml ).
(ii) Condition 1 (Temperture):

• Place plate A in a warm area, such as near a sunny window or under a lamp.
• Place plate B in a cooler area, such as a shaded part of the room.
• Keep plate C at room temperature as a control.

(iii) Condition 2 (Air Movement):

• Set up a fan or hairdryer to blow gently over plate A.
• Do not use any air movement on plate B.
• Keep plate C in room where no air movement as a control.

(iv) Condition 3 (Humidity):

• Increase humidity around plate A by placing a damp cloth nearby.
• Keep the humidity normal around plate B.
• Keep plate C at normal room humidity as a control.

(v) Start the timer as soon as you set up the conditions.

Observation:

Check and record the time taken for the water in each plate to evaporate completely.

Table 8.4: Recorded Data of the Investigation

Here are the values for the time taken for complete evaporation under different conditions:

Condition that is changed	Time taken for com-plete evaporation
Temperature (Warm area: 35° C)	2 hours
Temperature (Cool area: 18° C)	6 hours
Air Movement (Fan on)	3 hours
Air Movement (No Fan)	5 hours
Humidity (Increased: 80% RH)	8 hours
Humidity (Normal: 50% RH)	4 hours

Interpretation of Results:

Temperature: Water evaporated faster in a warm area (2 hours) compared to a cooler area (6 hours). This shows that higher temperatures increase the rate of evaporation.

Air Movement: With a fan on, the water evaporated in 3 hours, while without the fan, it took 5 hours. Increased air movement speeds up evaporation.

Humidity: In an area with higher humidity (80 % RH), water took 8 hours to evaporate, whereas in normal humidity (50 % RH), it evaporated in 4 hours. Higher humidity slows down evaporation.

These observations align with the principles of evaporation and demonstrate how different environmental factors can impact the process.

Activity 8.8 (Page-155)

Let us Explore

In Activity 8.8, we explore more on how environmental conditions such as sunlight, shade and air movement affect the rate of water evaporation. By comparing the time taken for water to evaporate under different circumstances, we can better understand the factors that influence this process. This activity also helps us relate these observations to everyday experiences, like drying clothes on different days.

Fig. 8.6: Evaporation of water in sunlight and in shade

Question 1.
What conclusions can you draw from Activity 8.8 and other similar experiences?
Answer:
Water evaporates faster from the cap kept in sunlight compared to the one kept in the shade.

• Clothes dry faster on a hot sunny day due to increased evaporation.
• Clothes also dry faster on a windy day because the movement of air speeds up evaporation.
• On a rainy day, clothes take more time to dry because the humidity in the air is higher, which slows down the evaporation process.

Question 2.
If you want to dry your clothes on a rainy day, how can you make it faster?
Answer:

• To dry clothes faster on a rainy day, you can place them under a fan to increase air movement.
• You could also use a dryer or place the clothes in a well-ventilated area to help reduce the moisture content in the air and speed up evaporation.

Question 3.
Do clothes dry faster or slower on a windy day?
Answer:
Clothes dry faster on a windy day. The increased movement of air helps to remove moisture from the surface of the clothes more quickly, speeding up the evaporation process.

Cooling Effect by Evaporation

Example: Earthen pots (matkas) keep water cool.
Concept: Evaporation from the surface of the pot removes heat, keeping the water inside cool.

Question 1.
Why is the water in the earthen pot so cold? I never observed water getting cold in a stainless steel pot. What do you think is the reason?
Answer:
The water in the earthen pot feels cold because water seeps through the tiny pores of the earthen pot and evaporates. This evaporation process requires heat, which is absorbed from the water inside the pot, leading to a cooling effect. This is why water stored in an earthen pot is cooler compared to water in a stainless steel pot.

Question 2.
How do you feel when you rub sanitiser on your hands?
Answer:
When you rub sanitiser on your hands, you might feel a cooling sensation. This happens because the alcohol in the sanitiser evaporates quickly, taking heat away from your skin and creating a cooling effect.

Activity 8.9 (Page-158)

Let us make Model

The “pot-in-pot cooler” is a traditional method used to keep perishable items cool and fresh without the need of electricity. Here’s a breakdown of the setup and its function:
Setup:

• Two pots: A larger pot and a smaller pot are used.
• Sand layer: The bottom of the larger pot is filled with a layer of sand.
• Smaller pot placement: The smaller pot is placed in the centre of the larger pot.
• Sand filling: The gap between the two pots is filled with more sand.
• Water addition: Water is poured into the sand area.
• Lid or jute sack: A lid or wet jute sack is placed on top of the smaller pot.

Cooling Effect:

• Evaporation: The water in the sand layer evaporates, absorbing heat from the surrounding area.
• Temperature reduction: This evaporation process cools down the sand and the smaller pot, creating a cooler environment inside.
• Insulation: The layer of sand and the lid or jute sack help to insulate the smaller pot, preventing heat entering from the outside.

Benefits of Using a Pot-in-Pot Cooler:

• Eco-friendly: It’s a natural and energy-efficient method of cooling.
• Cost-effective: It doesn’t require electricity or batteries.
• Portable: It can be easily moved and used in various settings.
• Effective: It can keep perishable items fresh for several days.

Question 1.
For how many days can vegetables and fruits be kept fresh in a pot-in-pot cooler?
Answer:
The duration for which vegetables and fruits can be kept fresh in a pot-in-pot cooler depends on various factors, including the type of products, the ambient temperature, humidity and the quality of the cooler itself. Generally, you can expect to keep fruits and vegetables fresh for 3-5 days under ideal conditions.

Question 2.
What are the conditions that can affect the number of days vegetables and fruits can be kept fresh?
Answer:
Several factors can influence the duration of freshness:

• Temperature: Higher ambient temperatures will reduce the cooling efficiency, leading to shorter storage times.
• Humidity: High humidity can promote spoilage. A drier environment is generally better for preserving fruits and vegetables.
• Product quality: The freshness and maturity of the product at the time of storage will affect its shelf life.
• Cooler design: The size, insulation and water retention capacity of the cooler can impact its cooling performance.

Question 3.
What can be used in place of sand for better cooling?
Answer:
Some alternative materials that can be used for better cooling include:

• Coconut coir: Coconut coir is a natural fiber that has excellent moisture-retention properties and can provide good insulation.
• Vermiculite: This is a lightweight, heat-resistant mineral that can help regulate temperature and humidity.
• Diatomaceous earth: This porous material can absorb moisture and help maintain a cool environment.

How do clouds give us rain?

Cloud Formation and Rain Condensation is a key process in the water cycle that helps return water from the atmosphere back to Earth’s surface in the form of precipitation. This process is essential for replenishing water sources and maintaining the balance of the Earth’s ecosystems.

Question 1.
How does condensation play a significant role in bringing evaporated water back to the Earth’s surface?
Answer:
Condensation occurs when warm, moist air rises and cools as it moves higher above the Earth’s surface.

At certain heights, the temperature drops enough for the water vapour in the air to condense into tiny droplets, often around dust particles. These droplets gather to form clouds. As more droplets combine, they create larger drops that become heavy and eventually fall as precipitation, such as rain. Under specific conditions, this precipitation may fall as hail or snow instead of rain.

Table 8.5: Understanding Rain

Process	Description	Observation
Evaporation	Water turns into vapour.	Water evaporates from surfaces.
Condensation	Vapour cools and forms droplets.	Clouds form in the sky.
Precipitation	Droplets fall as rain.	Rain falls from clouds.

Activity 8.10 (Page-158)

Let us engage in a group activity

Activity 8.10 is designed to demonstrate the role of dust particles in the formation of clouds. This hands-on activity helps students understand how tiny particles in the atmosphere contribute to cloud formation, a crucial part of the water cycle.

Question 1.
What materials are needed for Activity 8.10 ?
Answer:
You will need a discarded 1L plastic bottle, about one cup of water and a small burnt piece of newspaper.

Question 2.
What do you observe after squeezing and releasing the bottle continuously for about 2-3 minutes?
Answer:
Initially, without the burnt newspaper, you may not observe much in the space above the water in the bottle. However, when you add the burnt piece of newspaper and repeat the squeezing process, you will observe some haziness (resembling clouds) above the water in the bottle.

Question 3.
What is the role of the burnt plece of newspaper in this activity?
Answer:
The burnt piece of newspaper provides very small invisible dust particles around which water vapour condenses. This condensation leads to the formation of clouds, which you observe as haziness inside the bottle.

Water Cycle

The water from the ocean and the Earth’s surface evaporates into the atmosphere as vapour and returns as rain, hail or snow, ultimately flowing back to the oceAnswer: This circulation of water is known as the water cycle.

Only a small portion of water available on the Earth is fit for use by plants, animals and humans.

Most of the water is in the oceans and it cannot be used directly.

We use water for drinking and for many other activities. The number of people using water is increasing with a rise in population.

The increasing demand for water causes its shortage in many parts of the world. Hence, it is very important to use water wisely and avoid wasting it.

Keywords :

Melting: The process by which a solid turns into a liquid when heated. Example: Ice melting into water.

Freezing: The process by which a liquid turns into a solid when cooled. Example: Water freezing into ice.

Evaporation: The process where a liquid turns into a gas or vapour. usually due to heat. Example: Water evaporating from a puddle.

Condensation: The process where a gas turns into a liquid when cooled. Example: Water droplets forming on the outside of a cold drink.

Surface Area: The measure of the extent of a surface. In the context of evaporation, a larger surface area increases the rate of evaporation.

Precipitation: Any form of water that falls from the atmosphere to the Earth’s surface, such as rain, snow, sleet or hail.

Water Cycle: The continuous process by which water moves from the Earth’s surface to the atmosphere and back, including processes such as evaporation, condensation and precipitation.

Curiosity Class 6 Science Book Solutions