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ScienceClass 9CBSE

‘Osmosis is a special kind of diffusion’. Comment.

Soln: Diffusion in liquids and gases is the movement of particles from low concentration to high concentration. Osmosis is the movement of particles from the low concentration to high concentration through the semi permeable membrane. This movement happens due to diffusion. Hence Osmosis is a special kind of diffusion.

ScienceClass 9CBSE

The non S I and S I units of some physical quantities are given in column A and column B respectively. Match the units belonging to the same physical quantity: (A) (B) (a) Degree Celsius (i) kilogram (b) Centimetre (ii) Pascal (c) Gram per centimetre cube (iii) metre (d) Bar (IV) kelvin Milligram (v) kilogram per metre cube

Soln: — (iv) Degree Celsius and kelvin are the units of — (iii) Centimetre and metre are the units of —(v) Gram per centimetre cube and kilogram per metre cube are the units of — (li) Bar and pascal are the units of - (i) Milligram and kilogram are the units of

ScienceClass 9CBSE

Match the physical quantities given in column A to their S I units given in column B: (A) (B) (a) Pressure (i) cubic metre (b) Temperature (ii) kilogram (c) Density (iii) pascal (d) Mass (iv) kelvin Volume (v) kilogram per cubic metre

Soln: — (iii) The SI unit of pressure is pastor (denoted by P). — (iv) The SI unit of temperature is -kelvin" (denoted by K). — (v) The SI unit of density is kilogram per cubic metre (kg/m3). — (if) The SI unit of mass is kilogram (kg). — (i) The SI unit of volume is

ScienceClass 9CBSE

Evaporation of a liquid at room temperature leads to a——— effect. (b) At room temperature the forces of attraction between the particles of solid substances are———than those which exist in the gaseous state. (c) The arrangement of particles is less ordered in the ——— state. However, there is no order in the ——— state. (d) ——— is the change of solid state directly to vapour state without going through the ———state. (e) The phenomenon of change of a liquid into the gaseous state at any temperature below its boiling point is called———.

Soln: Cooling Stronger Liquid, gaseous Sublimation, liquid Evaporation

ScienceClass 9CBSE

A sample of water under study was found to boil at 102°C at normal temperature and pressure. Is the water pure? Will this water freeze at 0°C? Comment.

Boiling point of pure water is 100 °C and melting point is 0°C at 1 atmospheric pressure. Here the water boils at 102 °C hence it is not a pure water and freezes at temperature below 0°C.

ScienceClass 9CBSE

In which of the following conditions, the distance between the molecules of hydrogen gas would increase? (i) Increasing pressure on hydrogen contained in a closed container (ii) Some hydrogen gas leaking out of the container (iii) Increasing the volume of the container of hydrogen gas (iv) Adding more hydrogen gas to the container without increasing the volume of the container (a) (i) and (iii) (b) (i) and (iv) (c) (ii) and (iii) (d) (ii) and (iv)

Answer is c) ii and iii Explanation To increase the intermolecular interaction either volume of Hydrogen gas should be reduced or container volume should be increase. By increasing the pressure or by adding Hydrogen without increasing container volume inter-molecular interaction would decrease. Water under study was found to boil at 102°C at normal temperature and pressure

ScienceClass 9CBSE

Which condition out of the following will increase the evaporation of water? (a) Increase in temperature of water (b) Decrease in temperature of water (c) Less exposed surface area of water Adding common salt to water

Answer is a) Increase in temperature of water Explanation: Increase in temperature of water increase the kinetic energy of the water which will make more particles to attain enough energy to convert into vapour state. This is how increase in temperature favours evaporation. On the other hand exposed surface is also responsible for the evaporation. Higher the exposed surface are higher will be the evaporation. When common salt is added to water then surface is occupied by the solvent as well as non-volatile solute particles. This make the escaping tendency of solvent particles decrease and thus the evaporation of water decreases. Hence options (b), (c) and (d) will decrease the evaporation of water.

ScienceClass 9CBSE

The boiling points of diethyl ether, acetone and n-butyl alcohol are 35°C, 56°C and 118°C respectively. Which one of the following correctly represents their boiling points in kelvin scale? (a) 306 K, 329 K, 391 K (b) 308 K, 329 K, 392 K (c) 308 K, 329 K, 391 K (d) 329 K, 392 K, 308 K

Answer is c) 308 K, 329 K, 391 K Explanation: Temperature in Celsius can be converted into temperature in kelvin by adding 273 to the Celsius value. Boiling points of diethyl ether, acetone and n-butyl alcohol are 308 K, 329 K, and 391 K respectively.

ScienceClass 9CBSE

Choose the correct statement of the following (a) Conversion of solid into vapours without passing through the liquid state is called sublimation. (b) Conversion of vapours into solid without passing through the liquid state is called vaporisation. (c) Conversion of vapours into solid without passing through the liquid state is called freezing. Conversion of solid into liquid is called sublimation.

Soln: Answer is a) Conversion of solid into vapours without passing through the liquid state is called sublimation. Explanation: Sublimations is a process in which a solid is converted into vapours without passing through liquid Vaporisation is a phase transition from liquid to Conversion of liquid to solid at substance’s freezing temperature is called as

ScienceClass 9CBSE

A few substances are arranged in the increasing order of ‘forces of attraction’ between their particles. Which one of the following represents a correct arrangement? (a) Water, air, wind (b) Air, sugar, oil (c) Oxygen, water, sugar (d) Salt, juice, air

Answer is c) Oxygen, water, sugar Explanation: Intermolecular force of attraction is less in gases than liquid and solid. Solids have higher intermolecular attraction compared to liquid. In the answer Oxygen is a gas which has lesser intermolecular attraction than water-a liquid and sugar- a crystalline solid.

ScienceClass 9CBSE

During summer, water kept in an earthen pot becomes cool because of the phenomenon of (a) diffusion (b) transpiration (c) osmosis evaporation

Soln: Answer is d) evaporation Explanation: Evaporation of water through pores of earthen pot reduces temperature of immediate surroundings. This makes the water cool after some time. Movement of water through plants and evaporation through its aerial parts is called tyranspiration. Diffusion is the movement of a substance from an area of higher concentration to area of lower concentration If molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one it is called osmosis.

ScienceClass 9CBSE

The property to flow is unique to fluids. Which one of the following statements is correct? (a) Only gases behave like fluids (b) Gases and solids behave like fluids (c) Gases and liquids behave like fluids Only liquids are fluids

Soln: Answer is c) Gases and liquids behave like fluids Explanation: In gases and liquids intermolecular force of attraction between the particles is less and they facilitate flow of these states of matter.

ScienceClass 9CBSE

Seema visited a Natural Gas Compressing Unit and found that the gas can be liquefied under specific conditions of temperature and pressure. While sharing her experience with friends she got confused. Help her to identify the correct set of conditions (a) Low temperature, low pressure (b) High temperature, low pressure (c) Low temperature, high pressure High temperature, high pressure

Soln: Answer is c) Low temperature, high pressure Explanation: To compress gas into liquid, low temperature and high pressure is required. Between the particles of gas there is lot of space. On applying pressure particles get closer and they start attracting each other to form a liquid. Lot of heat is generated when gas is compresses hence it is necessary to cool it. Cooling lowers the temperature of compressed gas and helps in liquefying it.

ScienceClass 9CBSE

Which one of the following sets of phenomena would increase on raising the temperature? (a) Diffusion, evaporation, compression of gases (b) Evaporation, compression of gases, solubility (c) Evaporation, diffusion, expansion of gases Evaporation, solubility, diffusion, compression of gases

Soln: Answer is c) Evaporation, diffusion and expansion of gases Explanation: Particles of matter are continuously moving as they possess kinetic energy. When temperature us raised particles of matter intermix with each other which is called diffusion. Evaporation means conversion of liquid state into vapour state. When we increase temperature molecules move and vibrate so quickly that they escape into the atmosphere in the form of vapours. Increase in temperature causes the molecules move faster this results in expansion of gases.

ScienceClass 9CBSE

A cube of side 5 cm is immersed in water and then in saturated salt solution. In which case will it experience a greater buoyant force. If each side of the cube is reduced to 4 cm and then immersed in water, what will be the effect on the buoyant force experienced by the cube as compared to the first case for water. Give reason for each case. (b) A ball weighing 4 kg of density 4000 kg m–3 is completely immersed in water of density 103 kg m–3 Find the force of buoyancy on it. (Given g = 10 m s–2.)

Buoyant force, F = Vpg p= Density of water, V = Volume of water displaced by the body Volume and density of an object decides its Buoyancy. Cube will experience a greater byoyancy in saturated solution. If cube is reduces to 4 cm on each side, volume of cube becomes less as the buoyancy will be reduced as buoyant force is directly proportional to volume. (ii) The magnitude of the buoyant force given by F = Vpg where V = Volume of body immersed in water or volume of water displaced, p = Density of liquid. [∴ Given, mass of a ball = 4 kg, density = 4000 kgm-3]. Hence Volume of solid = 𝑀𝑎𝑠𝑠 𝐷𝑒𝑛𝑠𝑖𝑡𝑦 = 4 4000 = 1 1000 Buoyancy F= Vpg == 1 1000 10N x 1000x10

ScienceClass 9CBSE

Two objects of masses m1 and m2 having the same size are dropped simultaneously from heights h1 and h2 respectively. Find out the ratio of time they would take in reaching the ground. Will this ratio remain the same if (i) one of the objects is hollow and the other one is solid and (ii) both of them are hollow, size remaining the same in each case. Give reason.

h1 = 1 gt21 2 h2 = 1 gt22 2 as x = o 𝑡1= √ℎ1 𝑡2 ℎ2 As the acceleration remain same ratio between two objects remain same. In this case acceleration does not depend upon mass and size.

ScienceClass 9CBSE

How does the force of attraction between the two bodies depend upon their masses and distance between them? A student thought that two bricks tied together would fall faster than a single one under the action of gravity. Do you agree with his hypothesis or not? Comment.

Force of attraction between two masses separated by distance r is given by Newton law of gravitation where F= Gm1m2 Where G is gravitational force and it is an universal constant. R2 Gravitational force is directly proportional to the product of the masses of two bodies and inversely proportional to the square of the distance between them. Bodies thrown from same height fall with same speed irrespective of their mass. This is due to acceleration due to gravity. g= GM Where M is mass R is radius of the earth R2 This equation shows that acceleration due to gravity depends on mass of the earth and radius of the earth. Henec tow brick tied will not fall faster than single one.

ScienceClass 9CBSE

The earth is acted upon by gravitation of Sun, even though it does not fall into the Sun. Why?

Soln: Sun provides enough centripetal force to keep earth in its orbit and the earth provides centrifugal force due to its motion. These two force balance each other which prevents earth from falling into sun.

ScienceClass 9CBSE

How does the weight of an object vary with respect to mass and radius of the earth. In a hypothetical case, if the diameter of the earth becomes half of its present value and its mass becomes four times of its present value, then how would the weight of any object on the surface of the earth be affected?

Soln: Let R and M be the radius and mass of the earth Then Weight of the object= M R2 Original weight W0= mg = mg M R2 Hypothetically 4m and R becomes R 2 Then, weight = mG 4M (𝑅) 2 2 =(16m g) M R2 = 10xW0 Weight will be 16 times.

ScienceClass 9CBSE

Calculate the average density of the earth in terms of g, G and R.

Soln: g= GM R2 M=gR2 G Density of earth D= 𝑀𝑎𝑠𝑠 𝑉𝑜𝑙𝑢𝑚𝑒 = Gr2 GxVe = gR2 G4πR3 3 = 3g 4µGR

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