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3.  Temperature and heat play very important role.
 All species can function properly only if its body is maintained at
a particular temperature.
 In fact life on Earth is possible because the Sun’s temperature.
 Understanding temperature and heat - understand the nature.
 Thermodynamics is a branch of physics which explains the
phenomena of temperature, heat etc.
 this chapter helps to understand the terms ‘hot’ and ‘cold’ and
heat from temperature.
 Heat and temperature are two different but closely related
parameters.

4.  Spontaneous flow of energy from the object at higher
temperature to the one at lower temperature is called heat.
 This process of energy transfer from higher temperature object
to lower temperature object is called heating.
 Due to flow of heat sometimes the temperature of the body will
increase or sometimes it may not increase.

7.  the temperature of hands is
increased due to work.
 Temperature of the chin is
increased due to heat transfer
from the hands to the chin.
 By doing work on the system,
the temperature in the system
will increase and sometimes
may not.
 Either the system can transfer energy to the surrounding by doing work on
surrounding or the surrounding may transfer energy to the system by doing
work on the system.
 For the transfer of energy from one body to another body through the process
of work, they need not be at different temperatures.

8.  Temperature is the degree of hotness or coolness of a body.
 Hotter the body higher is its temperature.
 The temperature will determine the direction of heat flow.
 The SI unit of temperature is kelvin (K).
 In our day to day applications, Celsius (˚C) and Fahrenheit (°F)
scales are used.
 Temperature is measured with a thermometer.

9. 460
672
460
0
80
0
15
.
273
15
.
373
15
.
273
32
212
32
100
0












 Ra
R
K
F
C
6
.
10
460
4
5
273
9
32
5







Ra
R
K
F
C

10. Scale Symbol
for each
degree
LFP UFP Number of
divisions
on the
scale
Celsius C 0C 100C 100
Fahrenheit F 32F 212F 180
Reaumer R 0R 80R 80
Rankine Ra 460 Ra 672 Ra 212
Kelvin K 273.15 K 373.15 K 100

12. Here k = Boltzmann constant = 1.381×10−23 JK−1
C = k N.
NA = Avogadro number = 6.023 ×1023mol-1
NAk=R (universal gas constant) = 8.314 J mol-1 K-1

15. Only 21% of N are oxygen.
The total number of
oxygen molecules
Number of oxygen
molecules

16. Here STP means
T=273 K or 0 °C)
P=1 atm or 101.3 kPa)
μ = 1 mol
R = 8.314 J mol-1 K-1
𝐕 =
(𝟏 𝐦𝐨𝐥) 𝟖. 𝟑𝟏𝟒
𝐉
𝐦𝐨𝐥 𝐊
(𝟐𝟕𝟑 𝐊)
𝟏. 𝟎𝟏𝟑 × 𝟏𝟎𝟓 𝐍 𝐦−𝟐

24.  Thermal expansion is the tendency of matter to change in shape, area, and
volume due to a change in temperature.
 All three states of matter (solid, liquid and gas) expand when heated.
 When a solid is heated, its atoms vibrate with higher amplitude about their
fixed points. The relative change in the size of solids is small.

25.  Liquids, have less intermolecular forces than solids and hence they expand
more than solids. This is the principle behind the mercury thermometers.
 In the case of gas molecules, the intermolecular forces are almost negligible
and hence they expand much more than solids. For example in hot air
balloons when gas particles get heated, they expand and take up more
space.
 The increase in dimension of a body due to the increase in its temperature is
called thermal expansion.
 The expansion in length is called linear expansion.
 Similarly the expansion in area is termed as area expansion and
 the expansion in volume is termed as volume expansion.

26. Unit of coefficient of expansion of solids is ˚C-1 or K-1

27. 𝛼𝑉 = 3𝛼𝐿
𝛼𝐴 = 2𝛼𝐿

30. 𝝆 =
𝒎
𝑽

33. Calorimetry means the measurement of the amount of heat released
or absorbed by thermodynamic system during the heating process.

37. Conduction :
 Process of direct transfer of heat through matter due to
temperature difference.
 When two objects are in direct contact with one another, heat
will be transferred from the hotter object to the colder one.
 The objects which allow heat to travel easily through them are
called conductors.
Thermal conductivity :
 ability to conduct heat.
 The quantity of heat transferred through a unit length of a
material in a direction normal to unit surface area due to a unit
temperature difference under steady state conditions is known
as thermal conductivity of a material.

38. Thermal conductivity :
 ability to conduct heat.
 The quantity of heat transferred through a unit length of a
material in a direction normal to unit surface area due to a unit
temperature difference under steady state conditions is known
as thermal conductivity of a material.
𝐐
𝐭
∝
𝐀∆𝐓
𝐋
K coefficient of thermal conductivity.
The SI unit of thermal conductivity is J s-1 m-1 K-1 or W m-1 K-1.

41. Convection:
 Process in which heat transfer is by actual movement of
molecules in fluids such as liquids and gases.
 Molecules move freely from one place to another.
 It happens naturally or forcefully.

46. T − Ts = e
−
a
ms
t+b1
T − Ts = e
−
a
ms
t
eb1
T = Ts+b2e
−
a
ms
t
𝐨𝐫
𝐝𝐓
𝐝𝐭
∝ − 𝐓 − 𝐓𝐒

47. Solution:
The hot water cools 8 °C in 3
minutes.
The average temperature of 92 °C
and 84 °C is 88 °C.
This average temperature is 61 °C
above room temperature.
𝐝𝐓
𝐝𝐭
∝ − 𝐓 − 𝐓𝐒
The hot water cools 5 °C in dt
minutes.
The average temperature of 65 °C
and 60 °C is 62.5 °C.
This average temperature is 35.5 °C
above room temperature.
𝟖 °𝑪
𝟑
∝ − 𝟔𝟏 °𝑪 1
𝟓 °𝑪
𝐝𝐭
∝ − 𝟑𝟓. 𝟓 °𝑪 2
1 ÷ 2

48. Every object emits heat radiations at
all finite temperatures (except 0 K) as
well as it absorbs radiations from the
surroundings.
Prevost theory states that all bodies
emit thermal radiation at all
temperatures above absolute zero
irrespective of the nature of the
surroundings.

49. σ = Stefan’s constant
= 5.67 × 10−8 W m−2 k−4
If a body is not a perfect black body,
E = e σ T4
Where ‘e’ is emissivity of surface.
Emissivity is defined as the ratio of
the energy radiated from a material’s
surface to that radiated from a
perfectly black body at the same
temperature and wavelength.
𝐞 =
energy radiated from a material’s surface
radiated from a perfectly black body
at the same temperature and wavelength.