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NCERT Solutions Curiosity Chapter 8 and 1478.2 Another Mystery — Activity 8.3: Let us experiment

Book page 146 Updated on2026-09-05

Q1.
Take cold water in a glass tumbler, add a few ice cubes, leave it undisturbed for five minutes and observe. Record your observations and the questions that arise in your mind in Table 8.1.
Answer

Here is a completed Table 8.1. Write your own observations in the same way — one column for what you see, one for what you wonder.

I observeI wonder
Tiny water droplets appear all over the outer surface of the tumbler.Where has this water come from, when I poured water only inside the tumbler?
The small droplets slowly join and become bigger drops, which then trickle down.Why do the small drops join together?
The outer surface feels cold and wet when I touch it.Is the glass leaking? Or is the coldness itself making the water appear?
A ring of water collects on the table below the tumbler.Will the water level inside go down by that much?
The ice cubes become smaller and finally melt.Does the melting of ice have anything to do with the drops outside?
The same thing happens with a metal container, but not with a tumbler of room-temperature water.So is a cold surface necessary for the drops to appear?
Why the book asks you to write questions too: in science, a good question is as valuable as a good observation. The last row above is the question that finally solves the mystery — it compares a cold tumbler with a warm one and points straight at the real cause.
Q2.
Suggest possible reasons explaining the appearance of water droplets on the outer surface of the glass tumbler. Discuss with your friends. Write down the possible reasons in Fig. 8.3.
Answer

Write down every reason that seems possible, even if you later find it wrong. That is how the four children in Fig. 8.3 and Fig. 8.4 work.

Possible reasonHow we can test itVerdict
Ice came out of the tumbler and melted on the outside.Watch the rim carefully; the ice cubes are clearly inside all the time.Wrong
Water has seeped out through the wall of the glass.Mark the water level with a marker and check it after 30 minutes.Wrong — the level does not fall
Water splashed out while the ice was being dropped in.Pour gently, wipe the tumbler dry, and then watch.Wrong — drops still appear
The tumbler was already wet from washing.Wipe it completely dry before starting.Wrong — drops still appear
Water vapour present in the air touches the cold glass and turns into water.Keep a second tumbler with water at room temperature beside it. No drops appear on that one.Correct
Why the last reason wins: it is the only one that explains all the observations at once — why the drops appear only on a cold surface, why they appear on metal as well as glass, why the level inside does not fall, and why more drops appear on a humid day than on a dry one.
Tip: When you write reasons in Fig. 8.3, write them as sentences that can be checked. "The glass is magic" cannot be tested; "water has seeped through the glass" can.
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