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Q.1 : In adiabatic process there is no exchange of heat between a system and it’s surroundings. True or false?
Ans. Yes
Q.2 : What is Isothermal process?
Ans. A process in which T is constant or dT = 0 is an isothermal process i.e., for such a process dU = 0 and hence an isothermal process is not accompanied by any change in internal energy
Q.3 : What is adiabatic process?
Ans. Any process carried out suddenly is an example of an Adiabatic process e.g., bursting of a cycle tube. Mathematically a process in which the system and surroundings do not exchange any heat with each other i.e. dQ = 0
Thermodynamics In Physics, Isolated System, Important Topics For JEE 2025
Thermodynamics In Physics : Explore the principles of thermodynamics in physics, encompassing the laws governing energy transfer, entropy, and the behavior of systems at varying temperatures. Understand the crucial concepts like the first, second, and third laws of thermodynamics, and their applications in engines, refrigerators, and various scientific phenomena.
Shrivastav 21 May, 2024
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Thermodynamics In Physics :
We will learn that Thermodynamics is concerned with the work done by a system and the heat it exchanges with its surroundings. Alternatively, it is the study of changes that occur in some part of the universe (we designate as the system) and then everything else (outside the system) is the surrounding. A real or imagined boundary may separate the system from its surroundings.
A collection of properties such as pressure, volume, temperature and some other properties to be discussed later characterize the thermodynamical state of a system. The laws of thermodynamics describe how the energy in a system changes and whether the system can perform any useful work on its surroundings. Various thermodynamics processes such as adiabatic, isothermal, isochoric etc are discussed in detail.
Isolated System In Thermodynamics
Isolated System In Thermodynamics :
Consider first an isolated system for which there is no heat exchange and no work is done on the external environment. In this case
Q
= 0 and
W
= 0, so from the First Law we conclude Δ
U
= 0
U
= constant
The internal energy of an isolated system is constant.
Isochoric (Constant-Volume) Process In Thermodynamics
A process in which volume remains constant. e.g., a gas heated in a rigid container i.e.,
V
= constant
In this case
So, no external work is done in an Isochoric process.
According to First law of Thermodynamics
i.e., in an isochoric process the entire heat supplied just increases the internal energy of the gas responsible for the increase in temperature of gas.
Also, we must note that, in case of an isochoric process volume of the system remains constant
i.e.,
V
= constant
Since the boundary of the system does not displace because volume is constant, therefore,
W
= 0.
The change in internal energy is given by
From Fist Law, We have
Q
=
W
+
Isobaric Process In Thermodynamics
In an isobaric process the pressure of the system remains constant
i.e.,
P
= constant
The work done is given by
Using gas equation
PV
=
nRT
We get,
W
=
P
0
(
V
f
–
V
i
) =
nR
(
T
f
–
T
i
)
Since the change in internal energy is independent of the path followed, therefore
Using First Law of Thermodynamics,
So, for isobaric process, we have
Isothermal Process In Thermodynamics
To a novice we can explain that any process taking place gradually can be taken to be an example of isothermal process e.g., melting process. Mathematically, a process in which
T
is constant or
dT
= 0 is an isothermal process i.e., for such a process
dU
= 0 and hence an isothermal process is not accompanied by any change in internal energy. So, the First Law of Thermodynamics takes the form
dQ
=
dW
i.e., the entire heat supplied just does an external work.
The equation of state governing isothermal process is
PV
= constant
For an isothermal process,
PV
= constant, so
d
(
PV
) = 0
PdV
+
VdP
= 0
(Slope)
isot
=
Work done in an Isothermal Process :
∙
Since
Where,
is called the
Expansion Ratio
.
Since
P
1
V
1
=
P
2
V
2
Since temperature of the system remains constant, therefore, there is no change in internal energy.
Using First Law of Thermodynamics,
Adiabatic process In Thermodynamics
Any process carried out suddenly is an example of an Adiabatic process e.g., bursting of a cycle tube. Mathematically a process in which the system and surroundings do not exchange any heat with each other i.e.
dQ
= 0
Equation Of State For An Adiabatic Process
∙
According to First Law of Thermodynamics
dQ
=
dU
+
dW
0 =
dU
+
dW
=
nC
v
dT
+
PdV
…(1)
For an Ideal Gas, we have
PV
=
nRT
d
(
PV
) =
nRdT
PdV
+
VdP
=
nRdT
…(2)
Using (2) in (1), we get
For an Adiabatic process the equation of state is/are
Work done in an Adiabatic Process
Since,
dQ
= 0
Further,
Since
P
2
V
2
=
nRT
2
and
P
1
V
1
=
nRT
1
∙
Work done by the system is equal to the decrease in internal energy.
∙
Work done on the system is equal to the increase in internal energy.
Different Thermodynamics Processes
Different Thermodynamics Processes :
Different Thermodynamics processes and their important points are given below in tubular form.
S.No.
Name of the process
Important points in the process
W
1
Isothermal
T
,
PV
,
U
= constant
Q
=
W
0
2
Isochoric
or
C
=
C
P
0
3
Isobaric
C
=
C
P
For any system
For an ideal gas
4
Adiabatic process
0
5
Cyclic process
Since,
T
i
=
T
f
or
Q
net
=
W
net
0
W
net
= area between cycle on
p
-
V
diagram
6
Polytropic process
pV
x
= constant
7
Free expansion in vacuum
U
,
T
and
pV
= constant
or
0
0
0
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