At Bodhiclasses, we believe science is not just about reading facts but observing, questioning, and understanding the world around us. Chapter 8, A Journey Through States of Water, introduces young learners to the fascinating transitions of water through its three states—solid, liquid, and gas—while encouraging them to connect these changes to real-life situations.
Below are the detailed answers to the reflective and application-based questions from the chapter.
1. Which of the following best describes condensation?
(i) The conversion of water into its vapour state.
(ii) The process of water changing from a liquid into
gaseous state.
(iii) The formation of clouds from tiny water droplets.
(iv) The conversion of water vapour into its liquid state.
Answer:
(iv) The conversion of water vapour into its liquid state.
Explanation: Condensation is the process where water vapour in the air turns back into liquid water, often observed as droplets on cool surfaces like a tumbler or leaves in the early morning.
2. Identify in which of the given processes, evaporation is very important—
Answer:
(i) Colouring with: (b) water colours
(ii) Writing on paper with: (b) ink pen
Explanation: Water colours need to dry on paper after application, which involves evaporation of the water content. Similarly, ink from ink pens contains water or alcohol that evaporates to leave the written text on paper.
3. We see green coloured plastic grass at many places these days. Space around natural grass feels cooler than space around the plastic grass. Can you find out why?
Answer: Natural grass contains water and supports evaporation, which absorbs heat and creates a cooling effect. Plastic grass lacks moisture and does not allow evaporation, thus retaining heat and feeling warmer.
4. Give examples of liquids other than water that evaporate.
Answer:
- Alcohol
- Perfume
- Nail polish remover (acetone)
- Petrol
- Aftershave or sanitiser
These liquids evaporate quickly because they have low boiling points and are volatile in nature, which makes them suitable for products needing quick drying.
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 help increase air movement, which carries away the water vapour as it forms, speeding up the evaporation process. Although fans don’t produce heat, they aid in quicker drying by reducing the humidity near the surface of wet clothes.
6. Usually, when sludge is removed from drains, it is left in heaps next to the drain for 3–4 days. Afterward, it is transported to a garden or a field where it can be used as manure. This approach reduces transportation cost of the sludge and enhances the safety of individuals handling it. Reflect upon it and explain how.
Answer: Leaving sludge to dry reduces its water content through evaporation, making it lighter and easier to transport. Dry sludge also poses less health risk to workers as it reduces bad odor and microbial growth, and makes it more suitable for use as manure in agricultural fields.
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:
- Drying clothes on a clothesline
- Water drying from utensils after washing
- Sweating and feeling cool under a fan
- Cooking processes like simmering or boiling
- Applying sanitiser on hands
Understanding evaporation helps in:
- Speeding up drying processes
- Designing better cooling systems (like using earthen pots)
- Conserving water by identifying unnecessary evaporation
- Enhancing ventilation for comfort and hygiene
8. How is water present in the solid state in nature?
Answer:
In nature, water exists in the solid state as:
- Snow on mountain tops
- Icebergs floating in oceans
- Hailstones during storms
- Glaciers in polar and high-altitude regions
These solid forms of water are essential components of the Earth’s hydrological cycle and help in regulating climate.
9. Reflect on the statement “Water is our responsibility before it is our right.” Share your thoughts.
Answer:
Water is a precious and limited resource. While we all have the right to access clean water, it is our responsibility to conserve and protect it for future generations. Wasting water, polluting rivers, or ignoring climate changes can lead to scarcity. Responsible usage, rainwater harvesting, and education are keys to preserving this vital resource.
10. The seat of a two-wheeler parked on a sunny day has become very hot. How can you cool it down?
Answer:
You can cool down the seat by:
- Pouring or sprinkling water on it (which then evaporates and cools the surface)
- Placing a damp cloth or towel over it
- Parking in a shaded area or covering the seat with a reflective cover
The evaporation of water absorbs heat, producing a cooling effect that makes the seat bearable to sit on.
