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CH#7 Q.NO. i. iii. v. vii. ix. Answer A B A B D Properties of Matter Answers of MCQS Q.NO. ii. iv. vi. viii. x. Answer C D C C A Exercise Short Questions Q.No.7.2 Ans. Q.No.7.3 Ans. Q.No.7.4 Ans. Q.No.7.5 Ans. Q.No.7.6 Ans. Q.No.7.7 Ans. Q.No.7.8 Ans. Q.No.7.9 Ans. Q.No.7.10 Ans. How kinetic molecular model of matter is helpful in differentiating different states of matter? According to kinetic molecular model of matter, matter is made up of particles called molecules. Matter in which molecules are closely packed is called solids. Matter in which molecules are loosely packed is called liquids. Matter in which molecules are much farther apart is called gases. Does there exist a fourth state of matter? What is that? Plasma is called fourth state of matter in which a gas occurs in its ionic state. Positive ions & electrons get separated in the presence of electric or magnetic fields. What is meant by density? What is its SI unit? π Density of a substance is defined as it mass per unit volume. Its formula is = . π −3 Its SI unit is kgm . Can we use a hydrometer to measure density of milk? Yes, we can use a hydrometer to measure density of milk. The hydrometer which is used to measure density of milk is called lactometer. Define the term pressure? The force acting normally per unit area on the surface of a body is called pressure. Its formula is F P= A Its SI unit is Nm-2 or Pascal (Pa). Show that atmosphere exerts pressure? Take an empty can with a lid & pour some water into it. Place it over flame. After some time, steam starts coming out, expelling air from the can. Remove the can from the flame. Close the can firmly by its cap. Now place the can under the tap water. It is observed that the can gets crushed because pressure exerted by the atmosphere. As cold water is poured over the can, steam inside it condenses to water , creating a very low pressure. Outside the can, large atmospheric pressure acts on it, crushing it. This experiment shows atmosphere exerts pressure in all directions. It is easy to fill air in the balloon but it is very difficult to remove air from a glass bottle. Why? It is easy to fill air in the balloon but it is very difficult to remove air from a glass bottle because pressure inside the bottle is less than atmospheric pressure. What is barometer? The instrument which measure atmospheric pressure is called barometer. One of the simple barometer is called the mercury barometer. Why water is not suitable to be used in barometers? Mercury is 13.6 times denser than water. At sea level, vertical height of water column would be 0.76m x 13.6=10.34m. Thus a glass tube more than 10m long is Q.No.7.11 Ans. Q.No.7.12 Ans. Q.No.7.13 Ans. Q.No.7.14 Ans. Q.No.7.15 Ans. Q.No.7.16 Ans. Q.No.7.17 Ans. Q.No.7.18 Ans. Q.No.7.19 Ans. Q.No.7.20 Ans. Q.No.7.21 Ans. Q.No.7.22 required to make a water barometer which is not possible. Hence water is not suitable to be used in barometers. What makes a sucker pressed on a smooth wall sticks to it? A sucker pressed on a smooth wall sticks to it because of air pressure. It sticks to the wall since the pressure outside the sucker is greater than that inside. Why does atmospheric pressure varies with height? Air is mixture of gases .The density of air in atmosphere is not uniform. It decreases continuously as we go up. The air becomes thinner & thinner as we go up. Hence the atmospheric pressure decreases as we go up. What does it mean when the atmospheric pressure at a place fall suddenly? A sudden fall in atmospheric pressure often followed by a storm, rain & typhoon to occur in few hours time. What changes are expected in weather if a barometer reading shows a sudden increase? A rapid increase in atmospheric pressure means that it will soon be followed by a decrease in atmospheric pressure indicating poor weather ahead. State Pascal’s law? Pressure, applied at any point of a liquid enclosed in a container, is transmitted without loss to all other parts of the liquid. Explain the working of hydraulic press? The object to be compressed is placed over the piston of large cross-sectional area A. The force F1 is applied on the piston of small cross-sectional area a. The pressure P produced by small piston is transmitted equally to the large piston and a force F2 acts on A which is much larger than F1. What is meant by elasticity? The property of a body to restore its original size and shape as the deforming force ceases to act is called elasticity. State Archimedes principle? When an object is totally or partially immersed in a liquid, an upthrust acts on it equal to the weight of the liquid it displaces. What is upthrust? Explain the principle of floatation? Upthrust: The upward force acting on the object when it is immersed in the liquid is called the upthrust of the liquid. Principle of floatation: A floating object displaces a fluid having weight equal to the weight of the object. Explain how a submarine moves up the water surface & down into water? It floats over water when the weight of water equal to its volume is greater than its weight. It has a system of tanks which can be filled with and emptied from seawater. When these tanks are filled with seawater, the weight of the submarine increases. As soon as its weight becomes greater than the upthrust, it dives into water and remains under water. To come up on the surface, the tanks are emptied from seawater. Why does a piece of stone sink in water but a ship with huge weight floats? A stone sinks because its weight is greater than the upthrust acting on it. A ship with huge weight floats because its weight is equal or less than the upthrust. What is Hooke’s law? What is meant by elastic limit? Ans. Q. Ans. Q. Ans. Q. Ans. Q.No.1 Within the elastic limit, stress is directly proportional to corresponding strain. Elastic limit is a limit within which a body recovers its original length, volume or shape after the deforming force is removed. Write down important features of kinetic molecular model of matter? 1. Matter is made up of particles called molecules. 2. The molecules remain in continuous motion. 3. Molecules attract each other. Find the density of water if the mass of 5 litre of water is 5 kg? m = 5kg V = 5 litre = 5× 10−3 m3 π =? π 5 π= = = 1000πππ−3 π (5 × 10−3 ) The mass of 200 cm3 of stone is 500 g. Find its density. m = 500g V = 200cm3 π =? π 500 π= = = 2.5πππ−3 π 200 Derive a relation for pressure in liquid? Consider a surface of area A in a liquid at a depth h as shown by shaded region in figure. The length of the cylinder of liquid over this surface will be h. The force acting on this surface will be the weight w of the liquid above this surface. If p is the density of the liquid and m is mass of liquid above the surface, then m = π × π½ ---------(i) A=π×π V=π×π×π V = A× π ---------(ii) Put value of V in eq.(i) m=π×π×π Q.No.2 Ans. State ARCHIMEDES PRINCIPLE? Derive a relation for upthrust of liquid? Statement: When an object is totally or partially immersed in a liquid, an upthrust acts on it equal to the weight of the liquid it displaces. Explanation: Consider a solid cylinder of cross-sectional area A and height h immersed in a liquid as shown in figure. Let h1 and h2 be the depths of the top and bottom faces of the cylinder respectively from the surface of the liquid, then h 2 - h1 = h If P1 and P2 are the liquid pressures at depths h1 and h2respectively and π is its density, then P1 = πgh1 P2 = πgh2 Let the force F1 is exerted at the cylinder top by the liquid due to pressure P1 and the force F2 is exerted at the bottom of the cylinder by the liquid due to P2. .: F1 = P1A = πg h1A F2 = P2 A = πg h2A .: F2 -F1 = πgh2A - πgh1A = πgA (h2-h1) Upthrust of liquid= πgAh = pgV Q.No.3: Ans. Explain the working of hydraulic press? Hydraulic press is a machine which works on Pascal’s law. Construction: It consists of two cylinders of different cross-sectional areas as shown in figure. They are fitted with pistons of cross-sectional areas a and A. Working : The object to be compressed is placed over the piston of large cross-sectional area A. The force F1 is applied on the piston of small cross-sectional area a. The pressure P produced by small piston is transmitted equally to the large piston and a force F2 acts on A which is much larger than F1. Pressure on piston of small area a is given by πΉ1 P= π Apply Pascal’s law, the pressure on large piston of area A will be the same as on small piston. πΉ2 P= π΄ Comparing the above equations, we get πΉ2 πΉ1 = π΄ π πΉ2 = πΉ1× π΄ π π΄ is greater than 1, hence the force F2 that acts on the larger π piston is greater than the force F1 acting on the smaller piston. Hydraulic systems working in this way are known as force multipliers. Since the ratio is Q.No.4: Ans. Define Young’s modulus? Derive its relation? Definition: The ratio of stress to tensile strain is called Young’s modulus. Explanation: Consider a long bar of length Lo and cross-sectional area A. Let an external force F equal to the weight w stretches it such that the stretched length becomes L. According to Hooke’s law, the ratio of this stress to tensile strain is constant within the elastic limit of the body. Mathematically , Young’s modulus = Y = πΊπππππ π»ππππππ πΊπππππ Let βL be the change in length of the rod, then βπ³ = π³ − π³π Stress = π = Tensile Strain = πΊ = Y= πΊπππππ Y= π π¨ π π¨ Y= Q.No.6: Ans. π¨ π³−π³π π³π = βπ³ π³π π»ππππππ πΊπππππ Y= Q.No.5: Ans. π / × βπ³ π³π π³π βπ³ ππ³π π¨βπ³ SI unit of Young’s modulus is Newton per square meter (Nm-2). Explain breaking system in vehicles? The braking systems of cars, buses, etc. also work on Pascal’s law. The hydraulic brakes allow equal pressure to be transmitted throughout the liquid. When brake pedal is pushed, it exerts a force on the master cylinder, which increases the liquid pressure in it. The liquid pressure is transmitted equally through the liquid in the metal pipes to all the pistons of other cylinders. Due to the increase in liquid pressure, the pistons in the cylinders move outward pressing the brake pads with the brake drums. The force of friction between the brake pads and the brake drums stops the wheels. State kinetic molecular model of matter (solid, liquid and gas forms). Kinetic molecular model is used to explain the three states of matter - solid, liquid and gas. Solids: 1. Solids such as a stone, metal spoon, pencil, etc. have fixed shapes and volume. 2. Molecules are closely packed in solids. 3. Their molecules are held close together by strong forces of attraction. 4. They vibrate about their mean positions but do not move from place to place. Liquids: 1. A liquid has a definite volume. A liquid has no definite shape, so it attains 2. 3. 4. 5. the shape of a container to which it is put. Molecules are loosely packed in liquids.. The distances between the molecules of a liquid are more than in solids. Thus, attractive forces between them are weaker. Like solids, molecules of a liquid also vibrate about their mean position but are not rigidly held with each other. Due to the weaker attractive forces, they can slide over one another. Gases: 1. Gases such as air have no fixed shape or volume. They can be filled in any container of any shape. 2. In gases, molecules are much farther apart than solids or liquids. 3. Their molecules have random motion and move with very high velocities. 4. Gases are much lighter than solids and liquids. 5. A gas exerts pressure on the walls of the container.
