Class 9th science chapter 1st NCERT solution exercise question answers

Class 9th science chapter 1st NCERT solution exercise question answers

Exercises

(For Conversion Process we must know,
Kelvin is an SI unit of temperature, where 0°C = 273 K approx.)

1. Convert the following temperatures to Celsius scale.

(a) 300 K
► 300 K = (300 - 273) °C
= 27 °C

(b) 573 K
► 573 K = (573 - 273) °C
= 300 °C

2. Convert the following temperatures to Kelvin scale.

(a) 25°C
►25 °C = (25 + 273) K
= 298 K

(b) 373°C
► 373 °C = (373 + 273) K
= 646 K

3. Give reason for the following observations.

(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.

Answer

(a) Naphthalene balls disappear with time without leaving any solid because of they undergoes sublimation easily i.e., the change of state of naphthalene from solid to gas takes place easily.

(b) Perfumes have high degree of vaporisation and its vapour diffuses into the air easily. Therefore, we can get the smell of perfume sitting several metres away.

4. Arrange the following substances in increasing order of forces of attraction between particles-- water, sugar, oxygen.

Answer

Oxygen, Water, Sugar.

5. What is the physical state of water at-

(a) 25°C
► Liquid State

(b) 0°C
► Solid State, can also be in liquid state(conditions required).

(c) 100°C
► Gaseous State can also be in liquid state(conditions required).

6. Give two reasons to justify-

(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.

Answer
(a) Water at room temperature is a liquid because it has fluidity also it has no shape but has a fixed volume that is, it occupies the shape of the container in which it is kept.

(b) An iron almirah is a solid at room temperature it has rigid and fixed shape.

7. Why is ice at 273 K more effective in cooling than water at the same temperature?

Answer

Ice at 273 K has less energy than water (although both are at the same temperature). Water possesses the additional latent heat of fusion. Hence, at 273 K, ice is more effective in cooling than water.

8. What produces more severe burns, boiling water or steam?

Answer

Steam has more energy than boiling water. It possesses the additional latent heat of vaporisation. Therefore, burns produced by steam are more severe than those produced by boiling water.

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