Chapter 1st हमारे आस-पास के पदार्थ (9th class)

 Question 1: 

Convert the following temperatures into the Celsius scale.

(a) 300 K (b) 573 K

Answer 1:

(a) 300 K = 300 – 273 = 27 0C

(b) 573 K = 573 – 273 = 300 0C

Question 2: 

Convert the following temperatures into the Kelvin scale.

(a) 25OC (b) 373OC

Answer 2:

(a) 25OC = 25 + 273 = 298 K

(b) 373OC = 373 + 273 = 646 K

Question 3: 

Give reasons for the following observations.

(a) Naphthalene balls disappear with time without leaving any solid.

(b) We can get the smell of perfume sitting several meters away.

Answer 3:

(a) Naphthalene shows the property of sublimation. Evaporation of naphthalene

takes place easily and so it disappears during course of time without leaving a

solid.

(b) Perfumes vaporize very fast and its vapours diffuse into air easily. That is why

we can smell perfume sitting several meters away.

Question 4: 

Arrange the following in increasing order of forces of attraction between the

particles – water, sugar, oxygen.

Answer 4:

Oxygen < Water < Sugar.

Question 5:

What is the physical state of water at —

(a) 25°C (b) 0°C (c) 100°C?

Answer 5:

(a) Liquid

(b) Solid and Liquid

(c) Liquid and Vapours

Question 6:

Give two reasons to justify:

(a) Water at room temperature is a liquid.

(b) An iron almirah is a solid at room temperature.

Answer 6:

(a) Water at room temperature is a liquid because it has fluidity and has definite volume but no definite shape.

(b) An iron almirah is a solid at room temperature because it is rigid and has a definite shape.

Question 7: 

Why is ice at 273 K more effective in cooling than water at the same temperature?

Answer 7:

Ice at 273 K is less energetic than water. It is because of the difference in the latent heat of fusion which is present in water at the same temperature in the form of extra energy.

Question 8:

What produces more severe burns, boiling water or steam?

Answer 8:

Steam produces more severe burns than boiling water. This is because steam has more energy than boiling water, present in it in the form of latent heat of vaporization.

Q.9 characterize particles of matter ?

Q.10Which property of the substance is reflected in the ability of a diver to cut through water in a swimming pool?

Q.11The smell of hot food can be detected from several meters away, but to smell the smell of cold food you have to go closer. Why is this so?

Q.12 Describe the physical properties of matter ?

 Q.13 what is crystallization?

Q.14 what is diffusion ?

Q.15 what is the temperature ?

Q.16 What is force ?

Q.17 What force acts between substances ?

Q.18 what is matter ?

Q.19how many types of substances are there ?

Q.20 states of matter ?

Q.21 Tell the characteristics of the substance?

Q.22 what is compression?

Q.23 what is volume ?

Q.24 what is the melting point ?

Q.25 what are the five elements ?

Q.26 what is boiling point ?

Q.27 tell the full name of lpg ?

Q.28 tell the full name of cng ?

Q.29 what is kinetic energy ?

Q.30 Does the gas completely fill the vessel in which it is kept? What is the reason?

Q.31 what is called density ?

Q.32 what is irregular motion ?

Q.33 what is pressure ?

Q.34 what is called mass ?

Q.35 what is liquidity ?

Q.36 Gas exerts pressure on the walls of the vessel. Explain the reason?

Q.37 We can easily move our hands in the air but to move our hands through a solid piece of wood we have to be proficient in karate? What is reason ?

Q.38 Generally the density of liquid is less than that of solid, but you must have seen a piece of ice floating in water. Find out why this happens.

Q.39 What is the melting point of ice?

The melting point at which ice — a solid — turns to water — a liquid — is 32°F (0°C).

Q.40 The temperature remains the same during the melting process of a solid. So where does the thermal energy come from?

When solid melts, the temperature remains the same, this is because the absorbed heat is utilized in breaking the forces of attraction between the particles and hence solid changes to a liquid state without changing in temperature.

Q.41 what is thermal energy ?

Thermal energy refers to the energy contained within a system that is responsible for its temperature. 

Q.42 What is heat called?

In colloquial use, heat sometimes refers to thermal energy itself. Thermal energy is the kinetic energy of vibrating and colliding atoms in a substance.

Q.43 what is dry ice ?

Dry ice is solid carbon dioxide (similarly to ice of water).It is called dry ice because itgoes from solid to gaseous state without going to liquid phase i.e sublimation(in which instead of solid to liquid to gas it goes through solid to gas).

Q.44 Explain the effects of temperature change ?

Temperature can change the kinetic energy of particles of a substance. At high temperatures, the kinetic energy of particles is very fast and at low-temperature particles move slowly. High temperature converts solids into liquids and liquids into gases.

Q.45 what is thermometer ?

A thermometer is an instrument that measures temperature. It can measure the temperature of a solid such as food, a liquid such as water, or a gas such as air.

Q.46 what is evaporation?

Evaporation is the process by which a liquid turns into a gas. It is also one of the three main steps in the global water cycle.

Q.47 explain the effects of pressure change ?

Physical state of matter can also be changed by increasing or decreasing the pressure. 

The gases can be changed into liquids by increasing the pressure. 

Solids can be changed into gases by decreasing the pressure. 

Gases can be liquefied by applying Pressure and Lowering Temperature.

Q.48 full form of atm ?

atmosphere

Q.49 Why should we wear cotton clothes in summer ?

Cotton easily absorbs sweat from the body. Cotton clothes have fine threads which easily allow air to pass through when compared to woollen clothes. With more air flowing through the clothes, the sweat from the body and clothes gets evaporated easily, which leaves the cooling effect.