Point function and Path function, quasi static process, Equilibrium, Temperature (concepts, scales, international fixed points and measurement of temperature), Constant volume gas thermometer and constant pressure gas thermometer, mercury in glass thermometer.

1. Thermodynamics
Fundamentals of
thermodynamics
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2. Prof. S. A. Dahake
Point function and Path function
A Point function (also known as state function) is a
function whose value depends on the final and initial
states of the thermodynamic process, irrespective of the
path followed by the process.
Example of point functions are density, enthalpy, internal
energy, entropy etc.
During the process if the value of variable depends on
end states, they are known as point function.
Al thermodynamics properties say pressure, volume,
temperature are point function.
Since a point function is only dependent on the initial or
final state of the system but not on path follow
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3. Prof. S. A. Dahake
Point function and Path function
A Path function is a function whose value depends on the
path followed by the thermodynamic process irrespective
of the initial and final states of the process.
It is clear from p-V diagram that, area under each curve
represents work for each process
For process A work done is b2A1a
For process B work done is b2B1a
For process C work done is b2C1a
Since area under each curve is different, the amount of
work obtain in each case will different and is not
function of end state 1 or 2.
Here magnitude of work depends on the path, hence
work is path function.
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4. Prof. S. A. Dahake
Quasi static process
From the Latin quasi, meaning 'as if’
A quasi-static process is a thermodynamic process that happens slowly enough for
the system to remain in internal thermodynamic equilibrium. An example of this is
quasi-static expansion, where the volume of a system changes so slowly that
the pressure remains uniform throughout the system at each instant of time during
the process.
If a process takes place at faster rate, then the intermediate condition can not be
defined. Therefore, an assumption is made such that the process is taking place at a
such rate that the intermediate condition can be defined and hence must be
represented on a thermodynamic property diagram.
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5. Prof. S. A. Dahake
Quasi static process
Quasi = almost, Static = Constant
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6. Prof. S. A. Dahake
Equilibrium
A system is said to be in thermal equilibrium when temperature in all point in
system is same.
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7. Prof. S. A. Dahake
Temperature
Temperature is a physical quantity that expresses
hot and cold.
There are three temperature scales in use
today, Fahrenheit, Celsius and Kelvin.
Fahrenheit temperature scale is a scale based on
32 for the freezing point of water and 212 for the
boiling point of water, the interval between the
two being divided into 180 parts. The 18th-
century German physicist Daniel Gabriel
Fahrenheit invent Fahrenheit scale.
°C
100
=
𝐹−32
180
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8. Prof. S. A. Dahake
Temperature
Celsius temperature scale also called centigrade
temperature scale, is the scale based on 0 for the
freezing point of water and 100 for the boiling point of
water. Invented in 1742 by the Swedish astronomer
Anders Celsius, it is sometimes called the centigrade
scale because of the 100-degree interval between the
defined points.
K = 273+°C
Kelvin temperature scale is the base unit of
thermodynamic temperature measurement in the
International System (SI) of measurement. It is defined
as 1/ 273.16 of the triple point (equilibrium among the
solid, liquid, and gaseous phases) of pure water. An
absolute temperature scale named for the British
physicist William Thomson, Baron Kelvin.
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9. Prof. S. A. Dahake
Constant volume gas thermometer & Constant pressure gas
thermometer
A constant volume gas thermometer usually consists of a bulb
filled with a fixed amount of a dilute gas which is attached to a
mercury manometer. The manometer is used to measure
variation in pressure. This thermometer works on the principle
of Law of Gay-Lussac.
The law states that when the temperature of an ideal gas
increases, there is a corresponding increase in pressure. Also,
when the temperature decreases, the pressure too decreases
correspondingly. This is how constant volume gas
thermometers traces the increase in temperature with the
change in pressure while the volume remains constant.
An apparatus of Constant pressure gas thermometer, based on
Charles law in which a rigid vessel is filled with a gas, usually
hydrogen or helium, at low pressure and its volume measured
as its temperature is increased while its pressure is maintained
constant. The device must be calibrated at two fixed points,
such as the ice and steam points.
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10. Thank You
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