- Concept of Heat and Temperature
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- Zeroth Law of Thermodynamics
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- Measurement of temperature
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- Ideal Gas Equation and Absolute Temperature
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- Thermal Expansion
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- Thermal stress
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- Specific Heat Capacity
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- Calorimetry
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- Change of phases
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- Solved Examples

In gas thermometer , a quantity of gas is placed in a constant volume container. Then we measure its pressure. To calibrate a constant volume gas thermometer, we measure pressure at $0^C$ and $100^C$. We now plot these points on a graph and draw straight line between these two points. From this graph we can read the temperature corresponding to other pressure. Figure below show the result of three such experiments with different gases.

It is found that when graph were extrapolated for temperature below $0^{\circ}C$, pressure comes out to be zero at $-273^{\circ}C$ and this is the lowest temperature. Lord kelvin suggested that instead of $0^{\circ}C$ which is the melting point of ice,$-273^{\circ}C$ should be regarded as the zero of the temperature scale. Such a scale of temperature is absolute scale of temperature and $-273.15^{\circ} C$ as absolute zero of this new scale and is denoted as $0K$ and steam point in this scale correspond to $373.15 K$. From various experiments it turns out that this temperature is same for many different gases, at least in the limit of very low gas density. In gas thermometer different gases are used for measuring high temperatures and temperature reading are found to be independent of the nature of the gas used.

Gas thermometer can also define Celsius scale. If $P_{0}$ is pressure of gas at ice point and $P_{100}$ is pressure of gas at steam point then temperature T corresponding to a pressure P of gas is defined by, $$T=\frac{(P-P_{0})100}{(P_{100}-P_{0})}$$

Most of the solid material expands when heated. Increase in dimension of a body due to increase in its temperature is called

\begin{equation} \frac{\Delta L}{L}=\alpha_{L}\Delta T \tag{2} \end{equation} or, \begin{equation} \Delta L=\alpha_{L}L\Delta T \tag{3} \end{equation} Constant $\alpha_L$ characterizes the thermal expansion properties of a particular material and it is known as

Similarly, we can define

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