Notes on Thermal Properties of Matter
Heat is the agent which produces in us the sensation of warmth and makes bodies hot. It is form of energy. The part of thermal energy which flows from one body to the other due to temperature difference is called heat.
Nature of heat:-
(a) The weight of a body remains the same weather it is heated or cooled.
(b) Heat flows from higher to lower temperature
(c) In any exchange of heat, heat lost by the hot body is equal to the heat gained by the cold body.
(d) Substances generally expand when heated
(e) A certain amount of heat known as latent heat is required to change the state of a body from solid to liquid or from liquid to gas without any change in temperature.
In accordance to dynamical theory of heat the sum total of translational, vibrational and rotational energies of the molecules of a system is called the thermal energy of the system .
Unit of Heat:-
(a) Calorie (cal):- It is the amount of heat required to raise the temperature of 1 gram of water through 1ºC.
(b) Kilocalorie (kcal):- It is the amount of heat required to raise the temperature of 1 kilo gram of water through 1ºC.
It is defined as the degree of hotness of a body.
Zeroth Law of Thermodynamics:-
It states that the two systems (A and B) which are separately in equilibrium with a third system (C) must also be in equilibrium with each other.
Absoluter Zero of Temperature:-
(a) Charle’s law:- Vt = V0(1+ t/273)
(b) Gay Lussac’s law:- Pt = P0(1+ t/273)
(c) Absolute zero of temperature is defined as the temperature at which a gas has zero volume and exerts zero pressure. It is that temperature at which molecular motion ceases.
(d) C∝√T, C = √[c12 + c22 +…….+ cn2]/n
Absolute gas scale or absolute scale of temperature:- It is that scale of temperature whose zero (i.e. 0ºK) = -273ºC
A centigrade degree is exactly equal to the absolute or Kelvin’s degree.
Conversion of temperature from one scale to another:-
C/100 = (K-273)/100 = (F-32)/180 = Re/80 = (Rα-492)/180
Here C, K, F, Re and Rα are respectively, the temperatures of same both on centigrade, Kelvin, Fahrenheit, Reaumer and Rankin scale, respectively.
F = [(9/5)C ]+32
K = C+273
Linear Expansion (longitudinal expansion):-
When the expansion due to heating takes place only along one direction, the expansion is said to be one dimensional and linear.
Coefficient of linear expansion (α):- Coefficient of linear expansion of the material of a rod is defined as the change in length per unit length, at 0ºC, per degree centigrade rise of temperature.
α = lt-l0/l0t
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