Chapter no 8 Physics|9thClass Short Q||tutoronlines

Chapter No 8

Thermal properties of Matter

Table of content:

Number of topics Name of topics
1 Temperature and heat
2 Thermometer
3 Specific heat capacity
4 Latent heat of vaporization
5 Evaporation
6 Thermal expansion
7 Latent heat of fusion

Thermal properties:

Thermal properties are those properties of a material which is related to its conductivity of heat. In other words, these are the properties that are exhibited by a material when the heat is passed through it. Thermal properties come under the broader topic of the physical properties of materials.
Thermal properties of material decide how it reacts when it subjects to heat fluctuation (excessive heat or very low heat, for example). The major components of thermal properties are:

1.Heat capacity
2.Thermal Expansion
3.Thermal conductivity
4.Thermal stress

Chapter short Questions

Q.1 Which of the following substances have greater average kinetic energy of its molecules at 10°C? (a) steel (b) Copper (c) water (d) mercury

Ans. Copper

Q.2 Every thermometer makes use of some property of a material that varies with temperature. Name the property used in?

Ans. Strip thermometers

Mercury Thermometers:

(a) In strip thermometers, we use colour variation.

(b) In mercury Thermometer, we use Uniform thermal expansion of liquids.

Q.3 How specific heat differs from heat capacity?
Ans.  Specific heat:

Specific heat of a substance is the amount of heat is required to Raise the temperature of one kg mass of that substance through the 1k. Its SI units is Jkg-¹k.

Heat capacity:

Heat capacity of a body is the quantity of thermal energy, it absorbs for one kelvin 1k increase in temperature.

Its SI units is Jk-¹.

Q.4 Give two use of cooling effects by evaporation?

Ans. (i) Evaporation of perspiration helps to cool our body.

(ii) It lowers the temperature of the body.

Q.5 How evaporation differs from vaporization?
Evaporation:

Evaporation is the changing of a liquid into vapor’s ( gaseous state) from the surface of the liquid without heating it.

Vaporization:

The process in which liquid converts into gas at its boiling point its called vaporization.

Exercise short Questions

Q.1 Why does heat flow from hot body to cool body?

Ans. Molecules, of hot body have greater kinetic energy than the molecules of cold body. Therefore, fast moving molecules give their energy to cold body. So we can say that heat flows from hot body to the cold body due to difference of temperature.

Q.2 Define the term heat and temperature?
Heat:

Heat is the energy that is transferred from one body to the other in thermal contact with each other as a result of the difference of temperature.

Temperature:

Degree of hot ness or cold ness of the body is a measure of its temperature.

Q.3 What is meant by internal energy of a body?

Ans. The sun of the kinetic energy and potential energy. Associated with the atoms, molecules and particles of a body is called the internal energy.

Q.4 How does heating affect the motion of molecules of a gas?

Ans. Oh heating the gas, the motion of the molecules become faster. So internal energy of the gas molecules increase.

Q.5 What is thermometer? Why mercury is preferred as thermometric substance?

The instrument which is used to the temperature is called a thermometer. Mercury is the preferred as thermometric substance because It has;

high boiling point.
low melting point.
does not wet glass.
Good conductor.
Visible
Has low specific heat capacity.
It has uniform thermal expansion.
It has low freezing point.

Q.6 Explain the volumetric thermal expansion?

Ans. The volume of a solid also change with the change in temperature is called volume thermal expansion or cubical thermal expansion.

Change in volume of a solid ∆V=V-V°

Change in temperature ∆T= T-To

∆V ∞ Vo∆T

∆V= BVo∆T

V – Vo   =BVo∆T

V=Vo(1+B∆T)

B=∆V/Vo∆T

Thus we can define the temperature coefficient of volume expansion B as the fractional change in its volume per kelvin change in temperature.

Q.7 Define specific heat. How would you find the specific heat of a solid?
Ans. Specific heat:

Specific heat of a substance is the amount of heat required to raise the temperature of 1kg mass of that substance through 1k.

Q.8 Define and explain latent heat of fusion?
Ans. Latent heat of fusion:

Heat energy required to change unit of mass of a substance form solid to liquid state at its melting point without change in its temperature is called latent heat of fusion.

When a substance is changed from solid to liquid state by adding heat, the process is called fusion.

Melting point or fusion point:

The temperature at which solid starts melting point and fusion point.

Freezing point:

The temperature at which a substance changes from liquid to solid state is called its freezing point.

Q.9 Define and explain latent heat of vaporization?
Ans. Latent heat of vaporization:

The quantity of heat that changes unit mass of a liquid completely, into gas at its boiling point without any change in its temperature is called its latent heat of vaporization.

Q.10 What is meant by evaporation? On what factors the evaporation of a liquid depends? Explain how cooling is produced by evaporation?
Ans. Evaporation:

Evaporation is the process that changes liquid water to gaseous water (water vapor).

Following are the factors on which velocity of wind depends:

Velocity of wind :

It is a common observation that clothes dry faster on a windy day. With the increase in wind speed; the particles of water vapour move away with the wind, decreasing the water vapour in surrounding.

Temperature of surrounding :

With the increase in temperature of surrounding, more number of particles get enough Kinetic Energy to go into the vapour state.

Surface area of liquid exposed :

Evaporation is a surface phenomenon. As the surface area increases, the rate of evaporation also increases. For example, while putting clothes for drying up we spread them out.

Humidity of surrounding :

Humidity is the amount of water vapour present in the atmosphere. The air around us cannot hold more than a definite amount of water vapour at a given temperature. If the amount of water in air is already high, the rate of evaporation decreases.

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