Class 9 Science Chapter 1 Objects Around Us Solutions
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Objects Around Us Solutions
Answers to Questions Within the Lesson(1)
1. Q. Which of the following are matter?
Chair, air, love, smell, hatred, almond, thought, cold drink, fragrance of perfume.
Ans: Chair, air, almond, cold drink.
2. Q. Give reason for the following observation: The smell of hot sizzling food can be sensed from several meters away, but to get the smell of cold food we need to go closer.
Ans: We know that all matter is made up of tiny particles and these particles are in constant motion. When particles of matter receive heat, their kinetic energy increases. As a result, they spread over a larger distance. Therefore, the smell of hot sizzling food travels far.
On the other hand, particles of cold substances do not move much, so their smell can be sensed only when we go near.
3. Q. A diver is able to cut through water while swimming. Which property of matter makes this possible?
Ans: This is possible because the interparticle force of attraction in water is weak.
4. Q. What are the characteristics of particles of matter?
Ans: The characteristics of particles of matter are:
(a) There is space between particles of matter.
(b) Particles of matter are in constant motion.
(c) Particles of matter attract each other.
Answers to Questions Within the Lesson(2)
1. Q. Density is defined as the mass per unit volume of a substance. Arrange the following substances in increasing order of density: air, smoke coming out of a chimney, honey, water, chalk, cotton, and iron.
Ans: In increasing order of density: edible oil < cotton < water < soil <brick < iron.
2. Q. (a) Prepare a table showing the differences in the characteristics of the three states of matter.
Ans: The three states of matter differ in their properties such as shape, volume, compressibility, fluidity, kinetic energy, and density.
Solids have definite shape and volume, are rigid and incompressible, and have the highest density and least kinetic energy.
Liquids have definite volume but no definite shape, are slightly compressible, and have moderate kinetic energy.
Gases have neither definite shape nor volume, are highly compressible, and have the highest kinetic energy and lowest density.
(b) Comment on the following: rigidity, compressibility, fluidity, shape, kinetic energy, and density.
Ans: Here are concise comments on each of the given properties in the context of states of matter:
Rigidity: Rigidity refers to the ability of a substance to maintain its shape when an external force is applied. Solids are rigid because their particles are tightly packed and cannot move freely, whereas liquids and gases are not rigid.
Compressibility: Compressibility is the ability of a substance to decrease in volume when pressure is applied. Gases are highly compressible due to large spaces between particles. Liquids are slightly compressible, while solids are almost incompressible.
Fluidity: Fluidity is the ability of a substance to flow. Liquids and gases can flow easily, so they are called fluids. Solids do not flow and hence do not
possess fluidity.
Shape: Shape refers to the external form of a substance. Solids have a definite shape, while liquids take the shape of the container they are kept in. Gases have no definite shape and spread out to fill the container completely.
Kinetic Energy: Kinetic energy is the energy possessed by particles due to their motion. Gas particles have the highest kinetic energy, liquid particles have moderate kinetic energy, and solid particles have the least kinetic energy.
Density: Density is the mass per unit volume of a substance. Solids generally have high density due to closely packed particles, liquids have moderate density, and gases have very low density because their particles are far apart.
3. Q. Give reasons:
(a) A gas fills the container completely in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(d) We can easily move our hand in air, but to move it through a piece of wood we need a karate expert.
Ans: (a) The particles of a gas have very weak forces of attraction between them. Therefore, they move freely in all directions and fill the container completely.
(b) Gas particles move randomly in all directions and collide with each other as well as with the walls of the container. These collisions exert force on the walls. The force exerted per unit area is called pressure.
(c) The particles of wood are closely packed and have a definite shape and volume. Therefore, a wooden table is a solid.
(d) The distance between particles in air is large and the force of attraction is weak, so we can move our hand easily through air. In wood, particles are closely packed with strong forces of attraction, so moving a hand through it requires great force.
4. Q. The density of liquids is generally lower than that of solids. Butice floats on water. Why?
Ans: Ice has a lower density than water. This is because the arrangement of water molecules in ice creates more space between them, making ice lighter than water. Therefore, ice floats on water.
Answers to Questions Within the Lesson(3)
1. Q. Convert the following temperatures into Celsius scale:
(a) 300 K
(b) 573 K
Ans: We know that 0°C = 273 K
(a) 300 K = (300 – 273) = 27°C
(b) 573 K = (573 – 273) = 300°C
2. Q. What will be the physical state of water at the following temperatures?
(a) 250°C
(b) 100°C
Ans: (a) At 250°C, water will be in gaseous state.
(b) At 100°C, water will exist in both liquid and gaseous states.
3. Q. Why does the temperature remain constant during the change of state of a substance?
Ans: During the change of state of a substance, the temperature remains constant because the heat supplied is used to overcome the forces of attraction between the particles rather than increasing their kinetic energy. This heat is known as latent heat. Therefore, there is no rise in temperature during the change of state.
4. Q. Suggest a method to liquefy atmospheric gases.
Ans: Atmospheric gases can be liquefied by increasing pressure and decreasing temperature.
Answers to Questions Within the Lesson(4)
1. Q. Why does a desert cooler cool better on a hot and dry day?
Ans: A desert cooler cools more effectively on a hot and dry day because the rate of evaporation increases at higher temperatures, and the dryness of air further enhances evaporation. As a result, more heat is absorbed from the surroundings during evaporation, producing a stronger cooling effect.
2. Q. Why does water in an earthen pot remain cool during summer?
Ans: An earthen pot has numerous tiny pores. Through these pores, water seeps out to the outer surface. The heat from the water inside is used for evaporation of this water. As a result, the remaining water inside the pot becomes cool.
3. Q. Why do we feel cold when acetone, petrol, or perfume is poured on the palm?
Ans: When acetone, petrol, or perfume is poured on the palm, their particles absorb heat energy from the skin and evaporate. This removal of heat
causes a cooling sensation on the palm.
4. Q. Why is it easier to drink hot tea or milk from a plate than from acup?
Ans: A plate has a larger surface area than a cup. Therefore, the rate of evaporation of tea or milk is higher in a plate than in a cup. As a result, the tea or milk cools faster in a plate, making it easier to drink.
5. Q. What type of clothes should we wear in summer?
Ans: We should wear cotton clothes in summer. Cotton absorbs sweat from our body and helps it to evaporate into the atmosphere. This process removes heat from our body and gives a cooling effect.
Exercise: Questions and Answers
1. Q. Convert the following temperatures into Celsius scale:
(a) 293 K
(b) 470 K
Ans: We know that 0°C = 273 K
(a) 293 K = (293 – 273) = 20°C
(b) 470 K = (470 – 273) = 197°C
2. Q. Convert the following temperatures into Kelvin scale:
(a) 25°C
(b) 373°C
Ans: We know that 273 K = 0°C
(a) 25°C = (273 + 25) = 298 K
(b) 373°C = (273 + 373) = 646 K
3. Q. Give reasons:
(a) Naphthalene balls disappear when left in the open for a few days.
(b) The smell of perfume can be sensed from a distance.
Ans: (a) Naphthalene is a sublimable (volatile) substance. Therefore, it changes directly from solid to vapour and disappears without leaving any residue.
(b) Perfume contains volatile substances that evaporate easily and carry fragrance. Due to the high kinetic energy) of their particles, the smell spread over a long distance.
4. Q. Arrange the following in increasing order of force of attraction between particles: water, sugar, oxygen.
Ans: Oxygen < Water < Sugar.
5. Q. What is the physical state of water at the following temperatures?
(a) 25°C
(b) 0°C
(c) 100°C
Ans: (a) At 25°C, water is in liquid state.
(b) At 0°C, water exists in both solid (ice) and liquid states.
(c) At 100°C, water exists in both liquid and gaseous states.
6. Q. Explain with reason:
(a) Water is liquid at room temperature.
(b) An iron almirah is solid at room temperature.
Ans: (a) At room temperature, liquids have no definite shape but have definite volume. Water has definite volume but no fixed shape; it takes the shape of the container in which it is kept. Therefore, water is a liquid.
(b) An iron almirah is solid because it is rigid and not compressible. It has a definite shape and volume.
7. Q. Why does ice at 273 K cool more than water at the same temperature?
Ans: When ice at 273 K melts, it absorbs latent heat from the surroundings to change its state into water. This absorption of extra heat makes the surroundings cooler. On the other hand, water at 273 K does not absorb latent heat. Therefore, ice produces more cooling than water at the same temperature.
8. Q. Which causes more severe burns, boiling water or steam?Ans: Steam causes more severe burns than boiling water because steam at 100°C contains not only the heat of boiling water but also the latent heat of vaporization. When steam condenses on the skin, it releases this extra heat, causing more damage.
Additional Questions & Answers
1. Q. What is matter? What is it made of?
Ans: The things that we see around us and use, which occupy space and have mass, are called matter. Matter is made up of tiny particles such as atoms and molecules.
2. Q. What is latent heat of fusion and latent heat of vaporization?
Ans: Latent heat of fusion: The amount of heat required to convert unit mass of a solid into liquid at its melting point without any change in temperature is called the latent heat of fusion. Latent heat of vaporization: The amount of heat required to convert unit mass of a liquid into vapour at its boiling point without any change in temperature is called the latent heat of vaporization.
3. Q. What is melting?
Ans: The process by which a solid changes into a liquid state is called melting.
4. Q. What is diffusion?
Ans: The process by which particles of one substance intermix with the particles of another substance due to the spaces between them is called diffusion.
5. Q. What is the melting point of a substance?
Ans: The temperature at which a solid substance changes into liquid at atmospheric pressure is called its melting point.
6. Q. What is boiling point? What is the SI unit of temperature?
Ans: The temperature at which a liquid starts boiling at atmospheric pressure is called its boiling point. The SI unit of temperature is Kelvin (K).
7. Q. What are the values of upper fixed point and lower fixed point?
Ans: The upper fixed point is 100°C and the lower fixed point is 0°C.
8. Q. What is the melting point of ice in Kelvin scale?
Ans: 273 K (more precisely 273.15 K).
9. Q. What is sublimation? Give an example.
Ans: Sublimation is the process in which a substance changes directly from solid to gaseous state or from gaseous to solid state without passing through the liquid state. Example: solid carbon dioxide (dry ice).
Multiple Choice Questions (MCQ)
1. What is matter?
(a) Anything that has no mass
(b) Anything that occupies space but has no mass
(c) Anything that has mass and occupies space
(d) Only living things
Ans: (c)
2. Which of the following is not a form of matter?
(a) Air
(b) Water
(c) Love
(d) Iron
Ans: (c)
3. Matter is made up of:
(a) Cells
(b) Particles
(c) Organs
(d) Tissues
Ans: (b)
4. The particles of matter are:
(a) At rest
(b) Always moving
(c) Very large
(d) Invisible only
Ans: (b)
5. Which state of matter has a definite shape and volume?
(a) Solid
(b) Liquid
(c) Gas
(d) Plasma
Ans: (a)
6. Which state of matter has no definite shape but has definite volume?
(a) Solid
(b) Liquid
(c) Gas
(d) All
Ans: (b)
7. Which state of matter has neither definite shape nor volume?
(a) Solid
(b) Liquid
(c) Gas
(d) All
Ans: (c)
8. The force of attraction between particles is strongest in:
(a) Gases
(b) Liquids
(c) Solids
(d) Plasma
Ans: (c)
9. The force of attraction between particles is weakest in:
(a) Solids
(b) Liquids
(c) Gases
(d) Ice
Ans: (c)
10. Which of the following is highly compressible?
(a) Solid
(b) Liquid
(c) Gas
(d) Ice
Ans: (c)
11. Diffusion is fastest in:
(a) Solids
(b) Liquids
(c) Gases
(d) Ice
Ans: (c)
12. The process of change from solid to liquid is called:
(a) Freezing
(b) Melting
(c) Sublimation
(d) Condensation
Ans: (b)
13. The process of change from liquid to gas is called:
(a) Melting
(b) Freezing
(c) Vaporization
(d) Sublimation
Ans: (c)
14. The process of change from gas to liquid is called:
(a) Evaporation
(b) Condensation
(c) Melting
(d) Sublimation
Ans: (b)
15. The temperature at which a solid melts is called:
(a) Boiling point
(b) Melting point
(c) Freezing point
(d) Room temperature
Ans: (b)
16. The temperature at which a liquid boils is called:
(a) Melting point
(b) Freezing point
(c) Boiling point
(d) Condensation point
Ans: (c)
17. The SI unit of temperature is:
(a) Celsius
(b) Fahrenheit
(c) Kelvin
(d) Joule
Ans: (c)
18. 0°C is equal to:
(a) 100 K
(b) 273 K
(c) 373 K
(d) 200 K
Ans: (b)
19. Evaporation causes:
(a) Heating
(b) Cooling
(c) Freezing
(d) Melting
Ans: (b)
20. Which factor increases the rate of evaporation?
(a) Low temperature
(b) High humidity
(c) Large surface area
(d) None of the above
Ans: (c)
21. Cotton clothes are preferred in summer because they:
(a) Reflect heat
(b) Absorb sweat
(c) Produce heat
(d) Are heavy
Ans: (b)
22. Ice floats on water because:
(a) Ice is heavier
(b) Ice is denser
(c) Ice is less dense than water
(d) Ice has no mass
Ans: (c)
23. Sublimation is:
(a) Solid to liquid
(b) Liquid to gas
(c) Solid to gas directly
(d) Gas to liquid
Ans: (c)
24. Example of sublimation is:
(a) Water
(b) Ice
(c) Naphthalene
(d) Oil
Ans: (c)
25. Diffusion occurs due to:
(a) Attraction
(b) Repulsion
(c) Motion of particles
(d) Size of particles
Ans: (c)
26. Gases exert pressure because:
(a) They are heavy
(b) They collide with container walls
(c) They are visible
(d) They are cold
Ans: (b)
27. Liquids take the shape of:
(a) Their own shape
(b) Container
(c) Air
(d) Heat
Ans: (b)
28. Solids are rigid because:
(a) Particles are far apart
(b) Particles move freely
(c) Particles are closely packed
(d) No force exists
Ans: (c)
29. The latent heat is:
(a) Heat that raises temperature
(b) Heat absorbed without temperature change
(c) Heat lost only
(d) No heat
Ans: (b)
30. Increase in temperature increases:
(a) Attraction
(b) Particle movement
(c) Density always
(d) Size
Ans: (b)
31. Gases fill the container because:
(a) Strong attraction
(b) Weak attraction
(c) No motion
(d) Heavy particles
Ans: (b)
32. Density is:
(a) Mass only
(b) Volume only
(c) Mass per unit volume
(d) Temperature
Ans: (c)
33. Which has the highest density?
(a) Air
(b) Water
(c) Iron
(d) Cotton
Ans: (c)
34. Which has the lowest density?
(a) Iron
(b) Water
(c) Air
(d) Honey
Ans: (c)
35. Boiling involves:
(a) Surface only
(b) Entire liquid
(c) No heat
(d) Only bottom
Ans: (b)
36. Evaporation occurs at:
(a) Only boiling point
(b) Any temperature
(c) Freezing point
(d) Absolute zero
Ans: (b)
37. The particles of liquids:
(a) Are fixed
(b) Move freely but less than gas
(c) Do not move
(d) Are far apart
Ans: (b)
38. The particles of solids:
(a) Move freely
(b) Vibrate in position
(c) Are far apart
(d) No attraction
Ans: (b)
39. Increasing pressure can:
(a) Convert gas to liquid
(b) Convert solid to gas
(c) Stop motion
(d) Reduce mass
Ans: (a)
40. Decreasing temperature can:
(a) Convert liquid to gas
(b) Convert gas to liquid
(c) Increase motion
(d) Break particles
Ans: (b)
