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The very first page of the chapter has a box called Think It Over . Now that the whole chapter is done, this is the right moment to open it — because every answer is already in your hands.
- How are the sweet white crystals of sugar obtained from tall green sugarcane plants? A crystal is a solid grain with a regular shape.
- How do doctors detect a disease like malaria from just two or three drops of blood?
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Why do suspended particles settle in muddy water over time, but not in milk?
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AnswerBecause muddy water is a suspension and milk is a colloid .Explanation
The particles of muddy water are larger than 1000 nm, so gravity pulls them down and they settle. The particles of milk are only 1 to 1000 nm, so they stay evenly spread through the whole mixture and never settle.
Same idea, different particle size — and size is what decides everything. -
How is evaporation different from boiling?
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AnswerEvaporation happens at any temperature and only at the surface. Boiling happens at a fixed temperature and throughout the liquid.Explanation
This chapter does not answer this directly, so this is a short reminder from your earlier classes. Evaporation is a slow surface process that can occur at any temperature. Boiling occurs only at the boiling point, and bubbles of vapour then form all through the liquid, not just on top.
Surface and any temperature versus bulk and one fixed temperature. -
Why do you see bright rays of sunlight when it passes through small gaps between the leaves of a dense tree?
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AnswerBecause of the Tyndall effect .Explanation
Dust and other fine particles hanging in the air scatter the sunlight in every direction. That scattering is what makes the path of the beam glow, so we see bright shining lines of light.
No dust in the air, no visible ray.
