We have discussed “First law of thermodynamics” and “second law of thermodynamics” in our previous post, where we have also seen the
limitations of first law of thermodynamics. Today we will try to understand here
the Zeroth law of thermodynamics.
Zeroth law of thermodynamics
In the year of 1931, R.H. fowler had provided one
law of thermodynamics which is termed as Zeroth law of thermodynamics and
according to this law
“If two systems are in thermal equilibrium
separately with a third system, then they will also be in thermal equilibrium
with each other”.
Let us consider we have system A, system B and
System C as shown in following figure.
If system A is in thermal equilibrium with system C
and system B is also in thermal equilibrium with system C. Then according to Zeroth
law of thermodynamics, system A and system B will also be in thermal
equilibrium with each other.
Let temperature of system A is TA, temperature
of system B is TB and temperature of system C is TC.
If TA = TC and TB =
TC
Then according to Zeroth law of thermodynamics, temperature
of system A will be equal with temperature of system B.
TA
= TB
Zeroth law of thermodynamics provides the basic of
temperature measurement. If two systems are brought in contact with each other,
how we will come to know the direction of heat transfer?
We can only predict the direction of flow of heat,
if we are having information of temperature of both systems. Temperature of
systems will tell us the difference between hot body and cold body. Once we
have information about the hot body and cold body, we can express the direction
of heat flow between both bodies when they will come in contact with each
other.
Zeroth law of thermodynamics explains the basis of
temperature measurement. With the help of this law, we can compare the
temperature of system A and system B with the help of third system i.e. C
without making thermal contact between system A and B.
For securing quantitative measurement of
temperature, one reference system will be used and simultaneously we will have
to select few physical properties of this system that changes with respect to
temperature and such properties will be termed as thermometric properties. Variation
in thermometric properties will predict the variation in temperature. Reference
system which is used here for determining the temperature will be termed as thermometer.
System C will be termed, in zeroth law, as thermometer in above example.
Thermometer and thermometric properties
There are six various types of thermometer as
mentioned here with their respective thermometric property.
Sr. No.
|
Thermometer
|
Thermometric property
|
Symbol
|
1
|
Constant
volume Gas thermometer
|
Pressure
|
P
|
2
|
Constant
pressure Gas thermometer
|
Volume
|
V
|
3
|
Electrical
Resistance thermometer
|
Resistance
|
R
|
4
|
Thermocouple
|
Electromotive
force
|
E
|
5
|
Mercury
in glass thermometer
|
Length
|
L
|
6
|
Radiation
thermometer
|
Intensity
of radiation
|
I
|
Do you have suggestions? Please write in comment box
We will start our discussion with third law of thermodynamics in next post.
Reference:
Engineering thermodynamics, by R.K Rajput
Engineering thermodynamics, by P.K Nag
Image courtesy: Google
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