Ch 7Thermal Properties of Matter — Class 11 Physics, concept-first.

Until this chapter, describing the equilibrium of a mechanical system or the motion of a body only ever needed three fundamental quantities: length, mass and time.

Heat is best understood as energy IN TRANSIT. When two bodies at different temperatures are brought into contact, energy flows from the hotter to the colder one; this flow continues until no further n…

To measure temperature scientifically we first need a reliable way to say when two systems are at the SAME temperature, even without touching them together.

Two further ideas complete the groundwork for thermometry: first, that there is a genuinely absolute (thermodynamic) temperature scale that does not depend on the properties of mercury, resistance wir…

Experiments on gases at low density show that, at constant pressure, the volume of a fixed quantity of gas is directly proportional to its temperature measured in °C; likewise, at constant volume, its…

The relationship among a gas's pressure, volume and (absolute) temperature is called the ideal gas equation. Using absolute temperature, the classical gas laws take particularly simple forms:

Matter normally expands when heated and contracts when cooled. In a solid, the atoms vibrate about fixed mean positions; heating makes them vibrate more vigorously, pushing neighbouring atoms slightly…

For a substance in the form of a long rod of length , a small temperature change produces a fractional change in length that is directly proportional to (Fig.

For a substance in the form of a flat plate of area , the fractional change in area for a small temperature change (Fig.

For a substance in the form of a cube (or any three-dimensional solid) of volume , the fractional change in volume for a small temperature change (Fig.

Because , and all describe the same underlying phenomenon (the same linear stretching of interatomic spacing) viewed along one, two, or three dimensions respectively, they are not independent -- they…

If equal masses of water and paraffin are heated for the same time by an identical heater (so both receive the same heat energy), paraffin's temperature rises roughly twice as much as water's.

If is the heat absorbed or released by a substance of mass undergoing a temperature change , its specific heat capacity is defined by so that if and , then : specific heat capacity is the heat needed…

Gases behave differently from solids and liquids when heated: even a small temperature change can be accompanied by a considerable change in BOTH volume and pressure.

Combining the ideas of mass, specific heat and temperature change into a single working formula gives the general HEAT EQUATION: i.e., heat received or given out equals mass times temperature change t…

While specific heat capacity is a per-unit-mass property of a SUBSTANCE, it is often more convenient to talk about the heat needed for a particular BODY of that substance, of whatever total mass it ha…

Calorimetry is the experimental technique for QUANTITATIVELY measuring heat exchange, carried out using a calorimeter (Fig.

Matter ordinarily exists in three states -- solid, liquid and gas -- and moving from one of these to another is a CHANGE OF STATE, driven by an exchange of heat between the substance and its surroundi…

Not every substance passes neatly through solid-liquid-gas in sequence. Some substances change directly from the SOLID state to the VAPOUR state (and back) WITHOUT ever passing through an intermediate…

A pressure-temperature (P-T) diagram, called a phase diagram, is a convenient way to see at a glance which phase (solid, liquid or vapour) a substance is in for any combination of pressure and tempera…

The words "gas" and "vapour" are often used loosely as if interchangeable, but they have a precise physical distinction rooted in a substance's CRITICAL TEMPERATURE -- the temperature above which no a…

Whenever a substance changes state, heat is either absorbed or released, WITHOUT any accompanying change in temperature -- exactly the flat plateaus seen in the heating curve of §7.8 (Fig. 7.9).

Heat can move from one point of a body (or from one body to another) by three fundamentally different mechanisms: CONDUCTION, in which heat passes molecule to molecule through a solid without any bulk…

Conduction is the process by which heat flows from the hot end to the cold end of a solid body WITHOUT any net bulk movement of the body's own particles.

Thermal conductivity is a qualitative measure of how readily a solid conducts heat through it -- a good conductor of heat has a HIGH thermal conductivity, a bad conductor (insulator) has a LOW one.

To quantify conduction precisely, consider a cube of side with two opposite faces, each of area , maintained at temperatures and () (Fig. 7.12(b)).

By direct analogy with electrical resistance (potential difference divided by current), the ratio of temperature difference to heat-flow rate is called the thermal resistance of a conducting slab or r…

Everyday design choices exploit thermal conductivity directly. Cooking utensils are made of a metal (a good conductor, so heat from the flame quickly reaches the food) but are fitted with handles of a…

Unlike conduction, where energy passes molecule-to-molecule while each particle stays near its own mean position, convection transfers heat by the actual BULK, BODILY movement of heated (energised) mo…

Two everyday applications rely directly on convection. In heating (or cooling) a room, a heater (or convector) heats the air immediately around it; this heated air, now less dense, rises, while cooler…

When a hot body simply sits in contact with still air (say, air around a burning log), the air removes heat from it through spontaneously-arising currents -- this is FREE (or NATURAL) convection; land…

Radiation is the transfer of heat energy from one place to another by the EMISSION of electromagnetic (EM) waves -- travelling in straight lines at the speed of light, -- WITHOUT heating whatever lies…

If a vessel of hot water is left on a table, it gradually cools. Newton was the first to systematically study how the rate at which a body loses heat to its surroundings depends on its temperature, in…