Extra 30 short questions and answers from the chapter:1 "Matter in Our Surroundings" for Class 9 CBSE Science:-
1. Define matter. Give two examples.
Answer: Matter is anything that has mass and occupies space. Examples: Air, Water.
2. What are the three states of matter? Give one example of each.
Answer:
Solid:
Ice
Liquid:
Water
Gas:
Oxygen
3. What are the characteristics of particles of matter?
Answer:
Particles of matter have spaces between them.
Particles are continuously moving.
Particles attract each other.
4. Why do gases diffuse faster than liquids?
Answer: Gases have more intermolecular spaces and weak intermolecular forces, allowing particles to move freely and diffuse faster than liquids.
5. What is diffusion? Give an example.
Answer: Diffusion is the movement of particles from a region of higher concentration to lower concentration. Example: The smell of perfume spreading in a room.
6. Why do solids have a fixed shape?
Answer: In solids, particles are tightly packed with strong intermolecular forces, restricting their movement and giving a definite shape.
7. Why can liquids take the shape of a container but not solids?
Answer: Liquids have weaker intermolecular forces than solids, allowing their particles to move freely and take the shape of a container.
8. Why do gases not have a fixed shape or volume?
Answer: The intermolecular forces in gases are very weak, and particles move freely, allowing gases to expand and fill any available space.
9. What is evaporation? Name two factors that affect it.
Answer: Evaporation is the process where a liquid changes into vapor at temperatures below its boiling point. Factors affecting evaporation:
Temperature
Surface area
10. Why does evaporation cause cooling?
Answer: During evaporation, particles absorb heat energy from their surroundings to change into vapor, lowering the temperature and causing cooling.
11. Define boiling point. What is the boiling point of water?
Answer: The boiling point is the temperature at which a liquid changes into gas at atmospheric pressure. The boiling point of water is 100°C (373 K).
12. Define melting point. What is the melting point of ice?
Answer: The melting point is the temperature at which a solid changes into liquid. The melting point of ice is 0°C (273 K).
13. What is latent heat of fusion?
Answer: The amount of heat required to convert 1 kg of solid into liquid at its melting point without changing temperature is called the latent heat of fusion.
14. What is latent heat of vaporization?
Answer: The amount of heat required to convert 1 kg of liquid into gas at its boiling point without changing temperature is called the latent heat of vaporization.
15. Why does water boil at a lower temperature on mountains?
Answer: Atmospheric pressure is lower at high altitudes, reducing the boiling point of water.
16. Why do we see water droplets on the outer surface of a glass containing ice-cold water?
Answer: The water vapor in the air cools and condenses on the surface of the cold glass, forming water droplets.
17. Why do people sprinkle water on rooftops in summer?
Answer: Water absorbs heat from the rooftop and evaporates, causing a cooling effect.
18. How does humidity affect the rate of evaporation?
Answer: Higher humidity means more water vapor in the air, reducing the evaporation rate.
19. Why do we feel cold after applying alcohol or perfume on our skin?
Answer: Alcohol and perfume evaporate quickly, absorbing heat from our skin, causing a cooling effect.
20. Define sublimation. Give two examples.
Answer: Sublimation is the process where a solid changes directly into gas without becoming liquid. Examples:
Camphor
Dry Ice (Solid CO₂)
21. What is plasma? Give one example.
Answer: Plasma is the fourth state of matter, consisting of ionized gases. Example: Sun and stars contain plasma.
22. Why do naphthalene balls disappear over time without leaving any liquid?
Answer: Naphthalene undergoes sublimation, directly changing from solid to gas without forming a liquid.
23. Why does a desert cooler work better on a hot, dry day?
Answer: On a hot, dry day, evaporation occurs faster, leading to better cooling.
24. Why do wet clothes dry faster on a windy day?
Answer: Wind increases the rate of evaporation by carrying away water vapor from the surface of clothes.
25. Why is ice at 0°C more effective in cooling than water at 0°C?
Answer: Ice at 0°C absorbs latent heat of fusion before changing into water, providing extra cooling.
26. What happens to the movement of particles when a solid is heated?
Answer: When heated, the kinetic energy of solid particles increases, causing them to vibrate more and break free into a liquid state.
27. Why is water stored in earthen pots in summer?
Answer: The earthen pot has small pores that allow water to evaporate, causing cooling.
28. How does increasing pressure affect the boiling point of a liquid?
Answer: Increasing pressure raises the boiling point because more energy is needed for particles to escape into gas.
29. Why is steam at 100°C more harmful than boiling water at 100°C?
Answer: Steam contains latent heat of vaporization, which releases more energy on condensation, causing severe burns.
30. Why do doctors advise using wet cloth strips on the forehead during high fever?
Answer: The water in the cloth absorbs heat from the body and evaporates, cooling the patient.
