Adsorbate

The gas or liquid that is accumulated over the surface of a liquid or solid is referred to as adsorbate.

Adsorbent

The solid or liquid on whose surface, molecules of other substance are adsorbed.  

Adsorption

It is the process of attracting foreign atoms or molecules on to the host liquid or solid substance. Any surface of a solid or liquid exhibit residual forces of attraction normal to surface; hence molecules or atoms impinging on surface are adsorbed.

Aerodynamics

It is branch of fluid dynamics which deals with study of forces and the resulting motion of objects, when air interacts with them.

Aerosol

It is a colloidal suspension of solid or liquid particles in a gas; smoke or fog. Usually aerosol is sealed in a metal container under pressure with an inert gas or other activating agent and released as spray or through nozzle.

After Glow

See Phosphorescence. 

Air Break Down

It is dielectric breakdown of air when intense electric field is applied between two electrodes. For instance, dielectric breakdown strength of dry air at STP between spherical electrodes is 33KV/cm.

Air

Mixture of gases with traces of water vapor, etc which makes up earth’s atmosphere. Composition is 78% Nitrogen, 21% Oxygen, 0.03% CO2, 0.00005% Hydrogen, 0.933% Argon, 0.0018% Neon, 0.0005 Helium, 0.0001 Krypton etc.  

Albedo

The fraction of the total light incident on a reflecting surface, especially a celestial body, which is reflected back in all directions, is called as Albedo.

Algorithm

A finite set of unambiguous instructions performed in a prescribed sequence to achieve a goal, especially a mathematical rule or procedure used to compute a desired result. Algorithms are basis for most computer programming.

Allobar

It is a form of an element differing in isotopic composition from naturally occurring form. 

Allotropy

It is the property of substance to exist in two or more different crystal structures.

Alloy

A metallic substance that is composed of two or more elements is called as alloy.

Alpha Iron

Name used in metallurgy for iron or solid solution with iron as main continent with a BCC (Body centered cubic) structure.

Alpha Particle Spectrum

The line spectrum formed due to emission of alpha rays from isotopes due to nuclear states transition.

Alpha Particle

Positively charged particle identical to Helium nucleus (i.e. two protons and two neutrons) emitted from radioactive substance having heavy nuclei. They are typically emitted due to transition in energy states of parent nucleus to form daughter nucleus.

Alternating Current

Current in which charge periodically reverses and average value is zero. It usually implies a sinusoidal variation of current and voltage.

Altitude

The height of an object with reference to sea level or ground level is called as altitude.