thermodynamics , JEE , PMT , 10+1

1. Physics by Harjeet Singh
9815910789

2. Thermodynamics
Thermodynamics
It is the branch of the physics which deals with
the conversion of heat in to useful work.
System
The part of the space under study is called
system.
Surroundings
The part of the space outside system is called
surrounding

3. Thermodynamics
Heat
It is taken as positive when It is supplied to the
system. It is taken as negative ,when taken out of
the system.
Work
Consider a gas enclosed in the cylinder piston
assembly. Gas is considered as the system. At
Initial , the piston is kept stationary by keeping
certain load on it .If we release the load , the
piston will move up.

4. Thermodynamics
Let the displacement of the piston is in upward
direction
dr
F
Work done by the upward force

5. Thermodynamics
Total work done
For the increase in volume increases.Work is taken as
positive , (dV is positive)
It is taken as negative if there is decrease in the volume
Here the pressure can be constant , or it can be the
function of the volume.

6. Thermodynamics
Thermodynamic process:
It is the process by which we can change the
system form initial state to final state is called
thermodynamic process.
Thermodynamic variables
The variables by which we can specify the
state of the system: pressure , temperature
and volume are the state variables.

7. Thermodynamics
P P
V
V
i
i
f f
1
2
3
There are many ways by which we can take the
gas from initial state to final state. If we plot a
graph between the pressure and the volume ,
which is called PV diagram.

8. Thermodynamics
Work done can be calculated as the area under
the PV graph. Greater is the area , greater is the
work done
As there are number of ways to take the
system from initial state to final state , heat may
or may not be involved , there are number of
ways of doing work , therefore the work and
heat are the path-dependent variables

9. Thermodynamics
P
V
dV
P
dW = PdV
Area of the strip under PV graph is small work, to calculate the total work ,
we will have to calculate the area under the PV graph

10. Thermodynamics
 Reversible Process
 Irreversible Process
 Cyclic Process
Thermodynamic processes

11. Thermodynamics
Reversible Process
Reversible Process is
the process if it can
be turned back such
that both the system
and the surrounding
return to their
original states ,with
no change anywhere
else in the universe.
P
V
i
f
Moving from i to f
Moving from f to i
PV diagram for the
process returning
to i

12. Thermodynamics
Ir-reversible Process
Ir-reversible Process is
the process if it can
not be turned back
to its original state.
P
V
i
f

13. Thermodynamics
Cyclic Process
Cyclic-Process is the
process if we move
from a initial position
to a final position
through one path but
return to the initial
position through a
different path
P
V
1
2

14. Thermodynamics
Work done during a
Cyclic Process
If we move form initial
state to final state
through path 1 , the
work done is the area
under the red graph.
As the volume is
increasing the work done
is positive,
P
V
1
2
i
f

15. Thermodynamics
Work done during a
Cyclic Process
If we move form state ‘f’
to state to state ‘i’
through path 2 , the
work done is the area
under the green graph, as
the volume is decreasing
the work done is
negative ,
P
V
1
2
i
f
Net work done is the area under i1f2i graph, the net
work is positive ( shown by black lines)

16. Thermodynamics
 Isothermal process
 Adiabatic process
 Isobaric process
 Isochoric process
Thermodynamic processes

17. Thermodynamics
Isothermal process
It is the thermodynamic process in which the
temperature of the system remains constant.
Equation of the process
As the ideal gas eqn.
P
V

18. Thermodynamics
Adiabatic process
It is the thermodynamic process in which the heat is neither
taken out or taken into the of the system
Equation of the process
P
V
Isothermal
process
Adiabatic
process
Adiabatic process is fast process
Greater is the slope of PV
graph, faster is the process

19. Thermodynamics
Iso -baric process
It is the thermodynamic process in which
the Pressure of the system remains
constant.
Iso -choric process
It is the thermodynamic
process in which the
Volume of the system
remains constant.
P
V
Isobaric process
Isochoric
process

20. Thermodynamics
Poly –tropic Process
Any process which s not a standard
process comes under the category of
Polytropic process
Process Equation

21. Thermodynamics
Internal Energy
Internal energy of a system is defined as the sum of
total kinetic energy of all the constituent particles
and sum of the potential energy of interaction
among these particles.
Internal energy does not include the potential
energy of interaction among system and the
surroundings or kinetic energy because of the
motion of the frame of reference in which the
system is considered.

22. Thermodynamics
 Internal energy of an ideal gas depends upon the
temperature and not on pressure and volume.
 For non-ideal gases, Internal energy of an ideal gas
depends upon the temperature and pressure.
Internal Energy

23. Thermodynamics
 For an ideal gas , intermolecular forces are
zero , so the corresponding potential energy is
zero.
 Internal energy is represented by U.
 For the mixture of gases, the internal energy is
sum of the internal energies of the component
gases.
Internal Energy

24. Thermodynamics
This law states that if bodies A & B are in thermal
equilibrium with third body C, Then they are in
thermal equilibrium with each other
or
A
C
B
Zeroth Law of thermodynamics
We can say that everybody has a property called
temperature.When two bodies are in thermal
equilibrium, their temperatures are equal

25. Thermodynamics
First Law ofThermodynamics
When we supply certain amount of the heat , A
part of it is used to increase the internal energy
and a part of it is used for work
dQ = dU +W
dQ is the amount of the heat supplied
dU is change in the internal energy
W is the amount of the work done

26. Thermodynamics
First Law ofThermodynamics
Iso thermal Process
As the there is no change in the temperature of the system ,
there is no change in the internal energy of the system ; dU = 0
Whole of the energy supplied is used for useful work.
dQ =W
Adiabatic Process
As no heat is supplied to / taken out of the system , dQ = 0.
dU + W =0  dU = -W
If the work done is positive , there is a decrease in the internal
energy of the gas which means temp. decreases and vice-versa

27. Thermodynamics
First Law of Thermodynamics
Adiabatic Process
No heat is supplied to / taken out of the system,
dQ = 0.
dU + W =0  dU = -W
If the work done is positive , there is a decrease in
the internal energy of the gas which means temp.
decreases and vice-versa

28. Thermodynamics
First Law ofThermodynamics
Iso-choric Process
As the there is no change in the volume of the
system , no work is done ;W = 0
Whole of the energy supplied is used change the
internal energy of the system
dQ = dU

29. Thermodynamics
First Law ofThermodynamics
Iso-baric Process
As the there is no change in the
pressure of the system.
dQ = dU + W

30. Thermodynamics
First Law ofThermodynamics
Free expansion
These are the adiabatic processes in which
no work is done on or by the system.
dQ = 0 ,W= 0  dU= 0