Ch 3Kinetic Theory of Gases and Radiation — Class 12 Physics, concept-first.

The state of a fixed mass of gas is completely specified by a small set of macroscopic quantities -- its pressure , volume , temperature , and internal energy -- and any equation relating these quanti…

A single stone thrown into the air has a motion that is straightforward to describe: Newton's laws of motion, applied to that one object, tell us exactly where it will be at any instant.

A gas that obeys the ideal gas equation at every pressure and every temperature is called an ideal gas.

The molecules of an ideal gas are in continuous, random motion of the same qualitative character as the Brownian motion studied earlier -- ceaseless, erratic, undirected motion with no molecule favour…

This section derives, from first principles of Newtonian mechanics, how the macroscopic pressure exerted by a gas arises from the microscopic motion and collisions of its molecules.

Equation from Section 3.5 can be rearranged to give the mean square speed of the gas molecules directly in terms of macroscopic quantities:

Equation can be rewritten as

The kinetic energy of a single molecule, expressed component-wise, is

In the discussion of translational kinetic energy above, the molecule was implicitly free to move anywhere in three-dimensional space, needing three coordinates (, , ) and three velocity components (,…

A monatomic gas such as helium consists of single atoms, and a He atom -- being, for these purposes, effectively a point mass -- has only 3 translational degrees of freedom, and no others.

When the temperature of a gas is raised even slightly, both its volume and pressure can change considerably depending on the conditions under which heating occurs.

Setup. Consider one mole of an ideal gas enclosed in a cylinder by a light, frictionless, airtight piston, with pressure , volume and temperature .

Heat can be transferred by three distinct modes: conduction, convection and radiation. Conduction and convection both require a material medium -- heat cannot flow by these routes through a vacuum.

Let be the total thermal energy incident on the surface of an object in some time interval, and let , , be the respective amounts of that energy which are absorbed, reflected and transmitted.

A body that absorbs the entire radiant energy incident on it -- i.e. in the notation of Section 3.10.1 -- is called an ideal or perfect blackbody.

A simple, practical laboratory arrangement for realising a near-perfect blackbody was designed by Ferry.

In 1792, Pierre Prevost published what is now called the theory of exchange of heat: every body, at every temperature above absolute zero (0 K), continuously radiates thermal energy, and simultaneousl…

The coefficient of emission, or emissivity, , of a given surface is defined as the ratio of that surface's emissive power to the emissive power of a perfect black surface, both measured at the same te…

Kirchhoff's law of thermal radiation connects a body's emissive power to its absorptive power, wavelength by wavelength, for a body in thermal equilibrium.

The radiant energy emitted per unit area per unit time by a blackbody is not spread out evenly across all wavelengths -- it depends both on the body's temperature and on the wavelength under considera…

One of the clearest quantitative features of the blackbody spectral-distribution curves (Section 3.14, observation 4) is that the wavelength at which a blackbody's emissive power is maximum is inverse…

This section makes precise exactly how much thermal radiation a blackbody emits, as a function of its temperature.

The chapter-end exercises of the Balbharati Physics Std-XII textbook for Kinetic Theory of Gases and Radiation, in the book's own printed order and grouping: five multiple-choice questions, five short…

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