Thermal Physics

Question 1

temperature is the property, which determines _______ . It is a scalar quantity. The SI unit of temperature Figur is kelvin (K). There are other commonly used units of temperature such as degree celsius (°C) and degree fahrenheit (°F).

Answer 1

the direction of flow of heat.

Question 2

The temperature measured in relation to absolute zero using the kelvin scale is known as _____. It is also known as the ______

Answer 2

absolute scale temperature
thermodynamic temperature

Question 3

unit of the thermodynamic scale of temperature is defined as the ______ part of the thermodynamic temperature of the triple point of water.

Answer 3

fraction of 1/273.16th

Question 4

A temperature difference of ______ is equal to that of 1K. Zero Kelvin is the absolute scale of temperature of the body.

Answer 4

1°C

Question 5

Fahrenheit and Kelvin:

Answer 5

[K] = (F+460) ×(5/9)

Question 6

Two or more physical systems or bodies are said to be in _________ if there is no net flow of thermal energy between the systems.

Answer 6

thermal equilibrium

Question 7

When a hot object is in contact with another cold object, a form of energy flows from the hot object to the cold object, which is known as

Answer 7

thermal energy

Question 8

Thermal energy is also known as ‘

Answer 8

heat energy’ or simply ‘heat’.

Question 9

The SI unit of heat energy absorbed or evolved is

Answer 9

joule (J)

Question 10

Characteristic features of heat energy transfer

Answer 10

1. Heat always flows from a system at higher temperature to a system at lower temperature.
2. The mass of a system is not altered when it is heated or cooled.
3. For any exchange of heat, the heat gained by the cold system is equal to heat lost by the hot system.
   Heat gained = Heat lost

Question 11

Calorie:

Answer 11

One calorie is defined as the amount of heat energy required to rise the temperature of 1 gram of water through 1°C.

Question 12

Kilocalorie:

Answer 12

One kilocalorie is defined as the amount of heat energy required to rise the temperature of 1 kilogram of water through 1°C.

Question 13

Though the SI unit of heat energy is joule, there are some other commonly used units.

Answer 13

Calorie
Kilocalorie

Question 14

When a certain amount of heat energy is given to a substance, it will undergo one or more of the following changes:

Answer 14

• Temperature of the substance rises.
• The substance may change its state from solid to liquid or from liquid to gas.
• The substance will expand when heated.

Question 15

This change in the dimension due to rise in temperature is called

Answer 15

thermal expansion of the object

Question 16

All forms of matter (solid, liquid and gas) undergo ____& on heating.

Answer 16

expansion

Question 17

For a given change in temperature, the extent of expansion is smaller in solids than in liquids and gases. This is due to the _____.

Answer 17

rigid nature of solids

Question 18

The different types of expansion of solid are listed and explained below:

Answer 18

1. Linear expansion
2. Superficial expansion
3. Cubical expansion

Question 19

linear or longitudinal expansion.

Answer 19

When a body is heated or cooled, the length of the body changes due to change in Its temperature. Then the expansion is said to be linear or longitudinal expansion.

Question 20

coefficient of linear expansion

Answer 20

The ratio of increase in length of the body per degree rise in temperature to its unit length is called as the coefficient of linear expansion The SI unit of Coefficient of Linear expansion is K-¹

Question 21

The equation relating the change in length and the change in temperature of a body is given below:

Answer 21

(∆L/L⁰)=aL ∆T

aL - alpha surfix L

Question 22

superficial or areal expansion.

Answer 22

If there is an increase in the area of a solid object due to heating, then the expansion is called superficial or areal expansion.

Question 23

coefficient of superficial expansion.

Answer 23

Superficial expansion is determined in terms of coefficient of superficial expansion. The ratio of increase in area of the body per degree rise in temperature to its unit area is called as coefficient of superficial expansion

(∆A/A⁰)=aA ∆T

Question 24

cubical or volumetric expansion.

Answer 24

If there is an increase in the volume of a solid body due to heating, then the expansion is called cubical or volumetric expansion.

Question 25

coefficient of cubical expansion

Answer 25

As in the cases of linear and areal expansion, cubical expansion is also expressed in terms of coefficient of cubical expansion. The ratio of increase in volume of the body per degree rise in temperature to its unit volume is called as coefficient of cubical expansion. This is also measured in K-¹ (∆v/v⁰)=av ∆T

Question 26

Coefficient of cubic expansion (K-¹ Aluminium

Answer 26

7*10-⁵

Question 27

Coefficient of cubic expansion (K-¹) Brass

Answer 27

6*10-⁵

Question 28

Coefficient of cubic expansion (K-¹) Glass

Answer 28

2.5*10-⁵

Question 29

Coefficient of cubic expansion (K-¹) Water

Answer 29

20.7*10-⁵

Question 30

Coefficient of cubic expansion (K-¹) Mercury

Answer 30

18.2*10-⁵

Question 31

The coefficient of cubical expansion of liquid is independent of temperature

Answer 31

whereas its value for gases depends on the temperature of gases

Question 32

for liquids, we can define

Answer 32

real expansion and apparent expansion

Question 33

_real expansion

Answer 33

If a liquid is heated directly without using any container, then the expansion that you observe is termed as real expansion of the liquid. = L3-L2

Question 34

Coefficient of real expansion

Answer 34

Coefficient of real expansion is defined as the ratio of the true rise in the volume of the liquid per degree rise in temperature to its unit volume. The SI unit of coefficient of real expansion is K-¹.

Question 35

apparent expansion of the liquid.

Answer 35

The expansion of a liquid apparently observed without considering the expansion of the container is called the apparent expansion of the liquid. L3-L1

Question 36

Coefficient of apparent expansion

Answer 36

Coefficient of apparent expansion is defined as the ratio of the apparent rise in the volume of the liquid per degree rise in temperature to its unit volume. The SI unit of coefficient of apparent expansion is K-¹.

Question 37

The three fundamental laws which connect the relation between pressure, volume temps and temperature are as follows:

Answer 37

1) Boyle's Law 2) Charles's law 3) Avogadro's law

Question 38

Boyle s law

Answer 38

When the temperature of a gas is kept constant, the volume of a fixed mass of gas is inversely proportional to its pressure. Ρα 1/V In other words, for an invariable mass of a perfect gas, at constant temperature, the product of its pressure and volume is a constant. (i.e) PV constant

Question 39

Charles's law (The law of volume)

Answer 39

Charles's law was formulated by a French scientist Jacques Charles. According to this law, When the pressure of gas is kept constant, the volume of a gas is directly proportional to the temperature of the gas. V α T or V/T= constant

Answer 40

Avogadro's law states ich that at constant pressure and he temperature, the volume of a gas is directly proportional to number of atoms or molecules present in it i.e. Vαn (or) V /n = constant

Question 41

Avogadro's number

Answer 41

Avogadro's number (NA) is the total number of atoms per mole of the substance. It is equal to 6.023 × 10²³/mol.

Question 42

Gases are classified as

Answer 42

real gases and ideal gases.

Question 43

real gases

Answer 43

If the molecules or atoms of a gases interact with each other with a definite amount of intermolecular or inter atomic force of attraction, then the gases are said to be real gases

Question 44

At very high temperature or low pressure, a real gases behaves as an ideal gases

Answer 44

because in this condition there is no interatomicor intermolecular force of attraction.

Question 45

If the atoms or molecules of a gas do not interact with each other, then the gas is said.to be an

Answer 45

ideal gas or a perfect gas.

Question 46

Actually, in practice, no gas is ideal. The molecules of any gas will have a certain amount of interaction among them. But, these interactions are weaker when the pressure is low or the temperature is high because the interatomic or intermolecular forces of attraction are weak in ideal gas.

Answer 46

Hence, a real gas at low pressure or high temperature can be termed as a perfect gas.

Question 47

The Boltzmann constant is defined to be exactly

Answer 47

1.380×10−23 J⋅K−¹.

Question 48

term as universal gas constant μNakB=R

Answer 48

8.31J mol-¹K-¹

Question 49

Ideal gas equation is also called as equation of state

Answer 49

because it gives the relation between the state variables and it is used to describe the state of any gas.

Question 50

Ideal gas equation, also called as equation of state is PV = RT. Here, R is known as universal gas constant whose value is

Answer 50

8.31 J mol-¹K-¹

Question 51

A container whose capacity is 70 ml is filled with a liquid up to 50 ml. Then, the liquid in the container is heated. Initially, the level of the liquid falls from 50 ml to 48.5 ml. Then we heat more, the level of the liquid rises to 51.2 ml. Find the apparent and real expansion.

Answer 51

Level of the liquid L₁ = 50 ml Level of the liquid L₂ = 48.5 ml Level of the liquid L3 = 51.2 ml Apparent expansion = L3 - L₁ = 51.2 ml-50 ml = 1.2ml Real expansion = L3 - L₂ = 51.2 ml - 48.5ml = 2.7ml So, Real expansion > apparent expansion

Question 52

Keeping the temperature as constant, a gas is compressed four times of its initial pressure. The volume of gas in the container changing from 20cc ({V1 cc) to V2} . Find the final volume V2

Answer 52

P1V1=P2V2 V2=(P1/P2)*V1 (P/4P)*20 Cm³ V2= 5cm³

Question 53

If a substance is heated or cooled, the change in mass of that substance is a) positive b) negative c) zero d) none of the above

Answer 53

Zero

Question 54

If a substance is heated or cooled, the linear expansion occurs along the axis of a) X or -X b) Y or -Y c) both (a) and (b) d)(a) or (b)

Answer 54

Both a and b

Question 55

Temperature is the average of the molecules of a substance a) difference in K.E and P.E b) sum of P.E and K.E c) difference in T.E and P.E d) difference in K.E and T.E

Answer 55

difference in T.E and P.E

Question 56

The temperature and heat are _______quantities

Answer 56

Scalar

Question 57

3. One calorie is the amount of heat energy required to raise the temperature of ____of water through____

Answer 57

1g 1k

Question 58

4. According to Boyle's law, the shape of the graph between pressure and reciprocal of volume is ______

Answer 58

Straight line

Question 59

For a given heat in liquid, the apparent expansion is more than that of real expansion

Answer 59

Flase

Question 60

According to Charles's law, at constant pressure, the temperature is inversely proportional to volume.

Answer 60

Flase the temperature is directly proportional to volume.

Question 61

Assertion: There is no effects on other end when one end of the rod is only heated. Reason: Heat always flows from a region of lower temperature to higher temperature of the rod.

Answer 61

Assertion is true but the reason is false.

Question 62

2. Assertion: Gas is highly compressible than solid and liquid Reason: Interatomic or intermolecular distance in the gas is comparably high

Answer 62

Both the assertion and the reason are true and the reason is the correct explanation of the assertion.

Question 63

Find the final temperature of a copper rod. Whose area of cross section changes from 10m² to 11 m² due to heating. The copper rod is initially kept at 90 K. (Coefficient of superficial expansion is 0.0021 /K)

Answer 63

T = 137.62K

Question 64

Calculate the coefficient of cubical expansion of a zinc bar. Whose volume is increased 0.25 m³ from 0.3 m³ due to the 3 change in its temperature of 50 Κ.

Answer 64

α = 1.111×10^-3 /K.

Question 65

If you keep ice at 0°C and water at 0°C either of your hands, in which hand you will feel more chillness? Why?

Answer 65

Because water has the hidden heat called latent heat Reason: The 0°C ice takes more heat from hand equal to mL, to convert 0°C Ice water, 0°C as compared to 0°C water of same mass.