An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The change in the temperature of a gas in the → throttling process.

→ Joule; → Thomson; → effect.

The British physicist Sir Joseph John Thomson (1856-1940), discoverer of the electron (1897), Nobel Prize in Physics (1906). → Thomson atom, → Thomson cross section, → Thomson effect, → Thomson scattering, → Joule-Thomson effect.

The earliest theoretical description of the inner structure of atoms whereby an atom consists of a sphere of positive electricity of uniform density, throughout which is distributed an equal and opposite charge in the form of electrons. The diameter of the sphere was supposed to be of the order of 10^-8 cm, the magnitude found for the size of the atom. → Rutherford atom.

→ Thomson; → atom.

The → cross section involved the → Thomson scattering of electromagnetic waves by a free electron. It is defined by: σ_T = 8πr_e²/3, where r_e is the classical → electron radius. Its value is 0.665 245 x 10^-28 m².

→ Thomson; → cross; → section.

The absorption or emission of heat when current is passed through a single conductor whose ends are kept at different temperatures. If current is passed from hotter end to colder end of a copper wire, then heat is evolved along the length of the wire. When current is passed from colder end to the hotter end, then heat is absorbed.

→ Thomson; → effect.

The classical, → non-relativistic scattering of photons by free charged particles. When an electromagnetic wave is incident on a charged particle, the electric and magnetic components of the wave exert a force on the particle, setting it into motion. As it accelerates, it in turn radiates in all directions. Such scattering is independent of wavelength and equal numbers of photons are scattered forward and backward. Thomson scattering occurs in stellar atmospheres and in any non-relativistic → plasma. Thomson scattering is normally taken as the minimum → opacity.

→ Thomson; → scattering.