NCERT solutions for class 9th // Science // chapter 1- Matter in our surroundings
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NCERT solutions for class 9th // Science // chapter 1- Matter in our surroundings
Chapter 1- Matter in our surroundings
Page No 3
Q1 which of the following are matter
Chair , air, love ,smell, hate, almond, thought, cold ,cold drink ,smell of perfume.
Ans- the things which occupy the space are called matter
Matter - chair ,air, almond ,cold drink,
Q 2. Give reason for the following observation the smell of hot sizzling food reaches you several meters away but get the smell from cold food you have to go close?
Ans - Particles of matter are continuously moving that they possess the kinetic energy If the temperature of solid rises the particles move faster diffusion increases so the smell of hot sizzling food reaches you several meters away
Q3. Diver is able to cut through water in a swimming pool which property of matter does this observation shows
Ans - The particles of matter have intermolecular space between them and that space let to diver the water and pass through it.
Q4. What are the characteristics of particles of matter?
Ans - Particles of matter shows three properties
- Particles of matter have space between them
- Particles of matter are continuously moving
- Particles of matter attract to each other.
Page No 6
Q1. The mass per unit volume of substance is called density (density = Mass / volume ) arrange the following in order of increasing density air, exhaust from chimneys ,honey ,water ,chalk, cotton and iron.
Ans - air, exhaust from chimneys , cotton , water , honey , chalk , iron
Q2. a) Tabulate the difference in the characteristics of state of matter
Ans -
b) Comment upon the following rigidity compressibility fluidity feeling a gas container shaped kinetic energy and density.
Ans - Rigidity- It is the property of matter to resist the change of its shape.
Compressibility- It is the property of matter in which its volume is decreased by applying force.
Fluidity - It is the ability of matter to flow.
Filling a gas container - On filling a gas takes the shape of the container.
Shape - It having definite boundaries around the matter.
Kinetic energy- It is the energy possessed by the particles of matter due to its motion
Density- It is the ratio of mass with per unit volume
Q3. Give reason.
a) A gas fills completely the vessel in which it is kept?
Ans - Because a gas have not a specific shape it take the shape of the container where it placed.
b) A gas exerts pressure on the walls of the container.?
Ans - Because a particles of matters continuously moving randomly so it hits the walls of container therefore it exert pressure on the walls of the container
c) Wooden table should be called a solid?
Ans- Because the wooden table have a specific shape ,distinct boundaries and fixed volume and have a negligible compressibility.
d) We can easily move our hand in air but to do the same through a solid block of wood we need a Karate expert?
Ans - Because the particles of air are loosely arranged particles of air have large space between them but wood has a little space and these are compactly arranged . The density of the solid is more than the air. So we can easily move our hand in the air but in solid wooden block we need a Karate expert
Q4. Liquids generally have lower density as compared to solid but you must have observed that ice float on water find out why.
Ans - Ice which is solid has vacant space between water molecules does making ice lighter than the water does ice float on the water.
Page No. 9
Q 1. Convert the following temperature to Celsius scale. a) 300K b) 573K
Ans - a) 300K = ( 300 - 273) = 27° C
b ) 573K = ( 573 - 273 ) = 300 ° C.
Q2. What is the physical state of water at a) 250° C b) 100° C
Ans. - At 250 C water at gases state but at 100 C water at both state liquid as well as gases after getting heat It start to change the state
3. For any substance why does the temperature remain constant during the change of state?
Ans When the change of state of the substance start then energy which is supplied is used up as a latent heat it means that it does not increases the kinetic energy of the particles it only used to the remove the inter particular particles force in particular state it brings about a change in state therefore the temperature becomes constant
Q4 . Suggest a method to liquefy atmospheric gases?
Ans - Effect of change of pressure is liquefy the atmospheric gases.
Page no. 10
Q1. Why does a desert cooler cool better on a hot dry day?
Ans- In desert cooler water is used .The humidity level in the atmosphere is low and so the evaporation rate of water is high so the cooling is caused during evaporation and the air which escape from the cooler is comparatively cold due to low humidity therefore it is quite effective in hot and dry day
Q2. How does the water kept in an earthen pot (Matka) become cool during summer?
Ans - Earthen pot have lot of pores on it .The water oozes out through it and when the water comes on the surface of pot . It evaporate and causing cooling effect these make the pot cold and the water inside the pot also cool by this process.
Q3. When we pour some acetone or perfume on our palm we get a cooling sensation.
Ans - The boiling point of the acetone and perfume are low when they poured on a palm it get energy from our palm and surrounding and instantly converted into vapors and this method of vaporization gives the cooling sensation to our palm.
Q4. Why can we SIP hot tea from a saucer faster than from a cup?
Ans - The surface area of saucer is more than the cup so the rate evaporation is faster .Thus evaporation in a saucer causing more cooling than in the cup so we are able to SIP hot tea or milk faster from this saucer than a cup
Q5 . Why should we wear cotton clothes in summer .
Ans - Cotton is a good absorbers so it absorb the heat energy from our body surface and evaporate sweat and making the body cool so we should work cotton clothes during summer
Exercise
Q1. Convert the following temperature to the Celsius scale
a) 293 Kelvin. b) 470 Kelvin
Ans - a) (293 K - 273K) = 20 K
b) (470 K - 273K) = 197K
Q2. Convert the following temperature to the Kelvin scale
a) 25°C. b) 373° C
Ans - a) (25 °C + 273K) = 298K
b) (373°C + 273K) = 646K
Q3. Give reason for the following observation
a) Naphthalene balls disappear with time without leaving any solid .
b) We can get the smell of perfume sitting several meters away.
Ans - a) Naphthalene ball shows the property of the sublimation so naphthalene ball evaporate easily and disappear during the course of time without leaving any solid.
b) perfume contain the volatile solvent that is alcohol they have large space between them and diffuses faster and can reach a people sitting several metres away.
Q4. Arrange the following substance in increasing order of forces of attraction between the particles water sugar oxygen.
Ans- Sugar ,water, oxygen
Q5. What is the physical state of water at
a) 25°C b) 0°C. c) 100° C
Ans - a) liquid b) solid but if get latent heat from surrounding then convert into liquid c) Liquid , but if get latent heat from surrounding then convert into gases
Q6. Give two reason to justify
a) Water at room temperature is a liquid
b) An iron almirah is a solid at room temperature.
Ans- a) freezing point of water is 0 °C while boiling point of water is100° C and room temperature is always more than 0 °C and less than 100° C so water is liquid at room temperature.
b) an iron almirah is solid at room temperature because it has a definite shape and volume like a solid at room temperature and it is rigid in nature
Q7. Why is ice at 273 K more effective in cooling than water at same temperature?
Ans - Ice at 273 K more effective in cooling than water because ice get more energy from surrounding to change the state while water get less energy from the surrounding so ice at 273 K more effective in cooling
Q8. What produces more severe burns , boiling water or steam?
Ans - Steam produces more severe burns because steam has more energy than boiling water it has additional latent heat of the vaporization so when it falls on the skin it condenced and produced more heat energy .
Q9. Name A ,B ,C ,D ,E and F in the following diagram showing change in its state.
Ans -
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