If the atoms or molecules of a gas do not interact with each other, then the gas is said to be an ideal gas or a perfect gas.

The expansion of liquid apparently observed without considering the expansion of the container is called the apparent expansion of liquid.

(i) Increase in length per unit of the length of the solid object per degree celsius rise in temperature is called 'coefficient of linear expansion'.
(ii) Its SI unit is per kelvin.
\(\frac { \triangle L }{ { L }_{ 0 } } ={ \alpha }_{ L }\triangle T\Rightarrow { \alpha }_{ L }\frac { \triangle L }{ \triangle T.L_{ 0 } } \)
ΔL - change in length
L₀ - original length
ΔT - change in Temperature
α_L - coefficient of Linear expansion

When an object is heated or cooled, if the length of the object changes due to change in the temperature then the expansion is said to be linear or longitudinal expansion.

(i) Temperature of the substance rises.
(ii) The substance may change its state from solid to liquid or liquid to gas.
(iii) The substance will expand when heated.

(i) Heat always flows from a system at higher temperature to a system at lower temperature.
(ii) The mass of a system is not altered when it is heated or cooled.
(iii) For any exchange of heat, the heat gained by the cold system is equal to heat lost by the hotter system.

It is defined as the fraction, 1/273.16 of the thermodynamic temperature of triple point of water.

The temperature measured in relation to absolute zero using the Kelvin scale is known as absolute temperature.

(i) Co-efficient of apparent expansion is defined as the ratio of the apparent rise in the volume of the liquid per degree rise in temperature to its unit volume.
(ii) Its SI unit is K^-1.

Charles's law is otherwise called as the law of volume. It states that, when the pressure of gas is kept constant, the volume of the gas is directly proportional to the temperature of the gas.
\(\mathrm{V} \propto {T}\)

When the temperature of a gas is kept constant, the volume of a fixed mass of  gas is inversely proportional to its pressure. \(\mathrm{P} \alpha \frac{1}{\mathrm{~V}}\)

(i) The ratio of increase in volume of the body per degree rise in temperature to its unit volume is called as co-efficient of cubical expansion.
(ii) SI unit is K^-1.
(iii) Co - efficient of cubical expansion can be expressed as \(\frac{\Delta V}{V_{o}}=\alpha_{v} \Delta T\)

One calorie is defined as the amount of heat energy required to raise the temperature of 1 gram of water through 1^o C.

Due to difference in conductivity, metals having high conductivity compared to wood. On touch with a finger, heat from the surrounding flows faster to the finger from metals and so one feels the heat. Similarly, when one touches a cold a metal the heat from the finger flows away to the surroundings faster.

During driving temperature of the gas increases while its volume remains constant. So according to Charles's law at constant V, P α T. ∴ Pressure of gas increases.