Matter Selina Class 8 Physics

Matter Class 8 Physics Selina Concise

Part A: Objective Type Questions

Part B: Short/Long Answer Type Questions

Part A: Objective Type Questions

Q1.  Write true or false for each statement (a) The temperature of a substance remains unaffected during its change of state. Answer: True. 

(b) Ice melts at 100°C. Answer: False. The ice melts at 0° by absorption of heat. 

(c) Water at 100°C has more heat than the steam at 100°C. Answer: False. 

(d) Evaporation of a liquid causes cooling. Answer: True. 

(e) Water evaporates only at 100°C. Answer: False. 

(f) Boiling takes place at all temperatures. Answer: False. 

(g) Evaporation takes place over the entire mass of the liquid. Answer: False. 

(h) The process of a gas converting directly into solid is called vaporization. Answer: False. The process of a liquid converting directly into gas is called vaporization. 

(i) At high altitudes water boils above 100° C. Answer: False.

(j) The melting point of ice is 0°C. Answer: True.

Q 2. Fill in the blanks:- (Answers in bold)

(a) Evaporation takes place at all temperature. 

(b) Freezing process is just reverse of melting.

(c) Sublimation is a process that involves direct conversion of a solid into its vapour on heating. 

(d) The temperature at which a solid converts into a liquid is called its melting point. 

(e) The smallest unit of matter that exists freely in nature is called molecule. 

(f) Molecules of a substance are always in a state of motion and so they possess kinetic energy. 

(g) Intermolecular space is maximum in gases less in liquids and the least in solids. 

(h) Intermolecular force of attraction is maxiumum in solids, less in liquids and the least in gases. 

Q 3.

4. Select the correct alternative:- (Answers in bold)

(a) The inter-molecular force is maximum in 1. solids  2. gases  3. liquids  4. none of the above 

(b) The inter-molecular space is maximum in 1. liquids  2. solids  3. gases  4. none of the above 

(c) The molecules can move freely anywhere in 1. gases  2. liquids  3. solids  4. none of the above 

(d) The molecules move only within the boundary of 1. liquids  2. gases  3. solids  4. none of the above 

(e) The temperature at which a liquid gets converted into its vapour state is called its 1. melting point  2. boiling point   3. dewpoint   4. freezing point. 

(f) Rapid conversion of water into steam is an example of 1. evaporation   2. freezing   3. melting   4. vapourization. 

(g) Evaporation takes place from the

 1. surface of liquid  2. throughout the liquid   3. mid-portion of the liquid.  4. bottom of liquid. 

(h) Boiling takes place from the 

1. the surface of the liquid   2. throughout the liquid.  3. mid-portion of liquid   4. none of the above. 

Part B: Short/Long Answer Questions:-

Question 1. Define the term matter. What is it composed of ? 

Answer: Anything which occupies space and has mass is called matter. Matter is composed of tiny particles called MOLECULES. 

Question 2. State three properties of molecules of a matter.

 Answer: 1. They are very small in size. 2. They have spaces between them. 3. They are in constant motion and they posses kinetic energy. 

Question 3. What do you mean by the inter-molecular spaces ? How do they vary in different states of matter ? 

Answer: INTER-MOLECULAR SPACES “The spacing between the molecules of matter is called Inter-molecular spaces.” The inter-molecular spaces is less in solids more in liquids and still more in gases. Explanation of inter-molecular space : Take water in a measuring cylinder say upto 80 ml. mark. Add 10 gm of salt to it. The volume in cylinder should increase. On dissolving salt we find volume remains same i.e. upto 80 ml mark. This is because there are spaces in water molecules and salt molecules occupy these spaces and volume remains the same. 

Question 4. What is meant by the inter-molecular forces of attraction ? 

Answer: How do they vary in solids, liquids and gases ? INTER-MOLECULAR FORCES OF ATTRACTION : “The forces of attraction between the molecules of matter is called the inter-molecular force of attraction.” This inter molecular force is maximum in solids, less in liquids and least in gases. 

Question 5. Which of the following are correct ? 

Answer: (a) Solids have definite shape and definite volume. True. Reason As the molecules here have negligible intermolecular distance between them and have maximum intermolecular force of attraction. (b) Liquids have definite volume but do not have definite shape. True. (c) Gases have definite volume but no definite shape. False. Correct Gases have neither definite volume nor a definite shape. (d) Liquids have definite shape and definite volume. False. Correct Liquids have a definite volume but not definite shape.