Thermal Properties of Matter

Most substances expand when heated: raising a body's temperature increases the amplitude of thermal vibration of its atoms, which increases their average separation. For a solid rod of original length $L_0$, this linear expansion is described by $L=L_0(1+\alpha \Delta T)$, where $\alpha$, the coefficient of linear expansion, is a material property with unit ${\mathrm{K}}^{-1}$.

A solid als

A change of state — melting (solid to liquid), vaporization (liquid to gas), or sublimation (solid directly to gas) — occurs, for a pure substance at a given pressure, at one sharply fixed temperature: its melting point or boiling point. Reversing the process (freezing, condensation) releases exactly the heat the forward change absorbed.

While a change of state is actually in progress

Heat moves from a hotter region to a cooler one by three distinct mechanisms. Conduction transfers heat through a medium — typically a solid — by successive collisions between vibrating lattice particles and, in metals, free electrons, without any bulk movement of the medium itself. Convection transfers heat by the actual bulk motion of a fluid: a heated liquid or gas expands, becomes less

Newton's law of cooling states that a body's rate of loss of heat — equivalently, its rate of fall of temperature — is proportional to the excess of its temperature over its surroundings, provided this excess is small: $-\frac{dT}{dt}=k(T-T_s)$, which integrates to an exponential approach to the surrounding temperature, $T-T_s=(T_0-T_s)e^{-kt}$. Most NEET numericals instead use its fi