Ch 8Heat and Thermodynamics — Class 11 Physics, concept-first.

Heat and temperature are part of everyday experience: every living thing depends on staying within a narrow temperature range to function at all, and life on Earth as a whole is only possible because…

This short lead-in sets the stage for the whole unit by insisting, before any formula is introduced, that heat and work are both processes of energy transfer, never quantities an object can be said to…

"Heat" names the energy that flows from a hotter object to a cooler one purely because of their temperature difference -- it is energy in transit, not a quantity a body possesses.

"Work," like heat, is a way energy is transferred from one body to another -- but crucially, work does not require the two interacting bodies to be at different temperatures at all.

Temperature measures the degree of hotness or coolness of a body -- the hotter a body, the higher its temperature -- and it is precisely this quantity that fixes the direction in which heat will spont…

This heading opens the first half of the unit, "Thermal Properties of Matter," which develops the everyday, macroscopic thermal behaviour of gases, liquids and solids -- starting from the ideal gas la…

For a fixed amount of gas at low density, two empirical laws combine into the ideal gas law. Boyle's law: at constant temperature, pressure and volume are inversely related, .

Different substances -- and different masses of the same substance -- take different amounts of heat to reach the same temperature rise, which motivates defining heat capacity (the heat needed to rais…

Thermal expansion is the tendency of matter to grow in length, area or volume as its temperature rises; gases expand the most (negligible intermolecular forces), then liquids (weaker forces than solid…

Unlike most liquids, which simply contract on cooling at every temperature, water shows anomalous expansion: between 0°C and 4°C it actually contracts as it is heated (equivalently, it expands as it i…

Matter changes between its three states -- solid, liquid, gas -- through five named processes: melting (solid→liquid), evaporation (liquid→gas), sublimation (solid→gas), freezing/solidification (liqui…

Calorimetry is the measurement of the heat released or absorbed by a system during a heating process. If a hot body is placed in contact with a colder one and no heat escapes to the surroundings, the…

There are three distinct modes by which heat physically moves. Conduction is direct transfer through matter in contact, from hot to cold, without bulk motion of the material -- quantified by thermal c…

Newton's law of cooling states that the rate at which a hot object loses heat is proportional to how much hotter it currently is than its surroundings: , where is the surrounding temperature (the nega…

This short main heading opens the "Laws of Heat Transfer" section, which turns specifically to radiation -- the one heat-transfer mode that needs no medium at all -- and develops three linked ideas ac…

Prevost's theory of heat exchange states that every object at a temperature above absolute zero continuously emits thermal radiation into its surroundings, while simultaneously absorbing radiation arr…

The Stefan-Boltzmann law states that the total heat radiated per second, per unit surface area, by a black body is directly proportional to the fourth power of its absolute temperature: where is the S…

Every hot object radiates across a whole spread of wavelengths at once, but always with one particular wavelength, , at which the radiated intensity is greatest.

This heading opens the second half of the unit -- "Thermodynamics" proper -- marking the shift from the everyday, largely qualitative thermal properties of sections 8.2-8.3 into a systematic, quantita…

Thermodynamics is the branch of physics describing the laws governing the interconversion of work and heat, built up over three centuries of experimental work by Boyle, Charles, Bernoulli, Joule, Clau…

Two bodies are said to be in thermal equilibrium with each other when they are at the same temperature, which then does not change with time -- and once thermal equilibrium is reached, there is no fur…

A system's state at equilibrium is described by thermodynamic (state) variables -- pressure, temperature, volume, internal energy, entropy -- whose values completely fix the equilibrium state, unlike…

The zeroth law of thermodynamics states that if two systems A and B are each separately in thermal equilibrium with a third system C, then A and B are also in thermal equilibrium with each other -- ma…

The internal energy of a thermodynamic system is the sum of the kinetic and potential energies of all its molecules, measured relative to the system's own centre of mass: , where (internal kinetic ene…

James Prescott Joule demonstrated experimentally, in the eighteenth century, that mechanical energy can be converted into internal energy and back again, disproving the earlier "caloric fluid" theory…

The first law of thermodynamics extends the law of conservation of energy to explicitly include heat: the change in a system's internal energy equals the heat supplied to it minus the work done by it…

A quasi-static process is an infinitely slow process in which a system's variables (, , ) change so gradually that the system remains, at every single instant, in thermal, mechanical and chemical equi…

When a gas held in a cylinder with a movable piston (Figure 8.21) expands quasi-statically, pushing the piston outward by a small distance , the small work it does is ; since the gas exerts force on t…

A P-V diagram (Figure 8.22) plots a system's pressure against its volume as it undergoes a process, and is the standard graphical tool of thermodynamics because the area under the traced curve, betwee…

This short heading introduces a fact unique to gases: unlike solids and liquids, which effectively have just one specific heat capacity, a gas has two distinct specific heat capacities, because heatin…

Gases have two distinct specific heat capacities. Specific heat capacity at constant pressure (): the heat needed to raise 1 kg of gas by 1 K while it is free to expand and keep pressure fixed (Figure…

Meyer's relation connects and for an ideal gas. Heating moles at constant volume by does no work, so all the heat raises internal energy: .

This short heading introduces the four specific, named thermodynamic processes developed across the rest of section 8.8: isothermal (constant temperature), adiabatic (zero heat exchange), isobaric (co…

An isothermal process keeps temperature constant while pressure and volume vary. Since with fixed, , so , and the process traces a hyperbola (an "isotherm," Figure 8.25) on a P-V diagram; a curve clos…

An adiabatic process has zero heat exchange, , so the first law reduces to : the gas expands only at the expense of its own internal energy (cooling), or is heated by external compression work done on…

An isobaric process occurs at constant pressure while temperature, volume and internal energy all vary.

An isochoric process holds volume fixed while pressure, temperature and internal energy vary. From with fixed, , giving a straight - line through the origin; on a P-V diagram, an isochoric process is…

A cyclic process is one in which a system, after a series of changes, returns exactly to its initial state; since internal energy is a state variable, this means the net change in internal energy over…

On a P-V diagram, a cyclic process traces a closed loop (Figure 8.39), and the net work done over one complete cycle equals the area enclosed by that loop.

The first law of thermodynamics, being simply energy conservation, does not forbid heat flowing "backward" from a colder object to a hotter one, or a car's frictional heat spontaneously reassembling i…

A thermodynamic process is reversible only if it is possible to exactly retrace its path in the opposite direction, so that both the system and its surroundings pass back through precisely the same se…

A heat engine is a device that takes in heat and converts part of it into useful work, repeating a cyclic process indefinitely.

A Carnot engine, proposed by Sadi Carnot in 1824, is a hypothetical, perfectly reversible heat engine operating between two fixed temperatures, with four idealised parts: a source at constant , a sink…

The Carnot engine's efficiency depends only on its two reservoir temperatures, not on the working substance.

Since for a Carnot engine, the quantity is called entropy -- a state variable, with the entropy received from the hot reservoir and the entropy given out to the cold reservoir; for a reversible (Carno…

A refrigerator is essentially a Carnot engine run in reverse (Figure 8.49): instead of extracting heat from a hot reservoir to do work, it uses external work (supplied by a compressor) to pump heat OU…

A consolidated, bullet-point restatement of every idea developed across the unit: heat is energy in transit (never a stored quantity) flowing hot-to-cold; work transfers energy without requiring a tem…

The concept map traces how every idea in the unit connects back to a small handful of root concepts. Starting from Heat, Work, Ideal gas law and Thermal expansion/Heat capacity (grouped under "Thermal…

The end-of-unit evaluation, structured in the standard four parts used throughout the TN Physics Volume 2 textbook: Section I, 15 Multiple Choice Questions with an answer key printed at the end, spann…

Sample papers and previous-year board questions for this subject.