Thermal-1-2. 1st Law of Thermodynamics.pdf

Thermal physics

1. WELCOME
Md Nazrul Islam
Associate Professor (Physics)
Bangladesh Army International University
of Science and Technology (BAIUST)

2. Thermal Physics
Physics I_PHY-111 (EEE)

3. 1
st
Law of Thermodynamics
Topic

4. Zeroth Law of Thermodynamics
First Law of Thermodynamics
Proof of dW= P dV
Applications of 1
st
Law of Thermodynamics
Whatever we will discuss

5. Whenanytwobodiesareeachseparatelyin
thermalequilibriumwithathird,thentheyarealso
inthermalequilibriumwitheachother.
A
C
B
Zeroth Law of Thermodynamics

6. Whenworkistransformedintoheatorheatis
transformedintowork,thenworkandheatis
directlyproportionaltoeachother.
First Law of Thermodynamics
IfQamountofheatisproducedduetothetotaltransformation
ofWamountofwork,thenJHWorQW  ,
J=Mechanicalequivalentofheat
=4.186Joulespercalorie
Scientist Joule established the relation between work and heat.

7. Whenheatissuppliedtoanysystem,thenapartof
thisenergyisusedtoincreasetheinternalenergy
ofthesystemandtherestenergyisusedto
performexternalwork.
First Law of Thermodynamics
IfduetosupplyofdQamountofheattoanysystem,the
changeofinternalenergyisdUandworkdoneisdW,thenPdVdUdQor
dWdUdQ


,
Scientist Clausius expressed this law in general form. It is a special form of principle of
conservation of energy.

8. Proof of dW= PdV




2
1
int
][,
V
V
dVPW
formegralIn
dVPdW
A
F
PdxAPdWor
dxFdW


9. IsothermalProcess
Temperatureofthesystemremainsconstant,asaresultinternal
energyremainsunchanged.i.e.,dU=0.
Incaseofisothermalprocess,1
st
lawofthermodynamicscanbe
expressedasdQ=dW.
AdiabaticProcess
Totalheatofthesystemremainsconstant.Noheatenters(or
leaves)inthesystemduringexpansionorcompression.i.e.,dQ=0.
Incaseofadiabaticprocess,1
st
lawofthermodynamicscanbe
expressedasdU+dW=0.
Applications of 1
st
Law of Thermodynamics

10. IsobaricProcess
Anisobaricprocessisathermodynamicprocessinwhichthe
pressureremainsconstant.
Simplestexamples:Theheatingofwaterinanopenvesseland
theexpansionofagasinacylinderwithafreelymovingpiston.
IsochronicProcess
Volumeofthesystemremainsconstant.i.e.,dV=0;dW=PdV=0.
Incaseofisochronicprocess,1
st
lawofthermodynamicscanbe
expressedasdQ=dU.
Applications of 1
st
Law of Thermodynamics