Glossary of Physics (A)

Acceleration: The rate of change of velocity with respect to time.

Acceleration due to gravity: The acceleration imparted to bodies by the attractive force of the earth or any other heavenly body.

Achromatic: capable of transmitting light without decomposing it into its constituent colors.

Acoustics: The science of the production, transmission and effects of sound.

Acoustic shielding: A sound barrier that prevents the transmission of acoustic energy.

Adiabatic: Any change in which there is no gain or loss of heat.

Afocal lens: A lens of zero convergent power, whose focal points are infinitely distant.

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

Alpha particle: The nucleus of a helium atom (two protons and two neutrons) emitted as radiation from a decaying heavy nucleus.

Alternating current: The electric current that changes its direction periodically.

Amorphous: Solids which have neither definite form nor structure.

Ampere: S.I. Unit of electric current, one ampere is the flow of one coulomb of charge per second.

Amplitude: The maximum absolute value attained by the disturbance of a wave or by any quantity that varies periodically.

Angle of contact: The angle between tangents to the liquid surface and the solid surface inside the liquid, both the tangents drawn at the point of contact.

Angle of incidence: The angle between the incident ray and the normal.

Angle of reflection: The angle between the reflected ray and the normal.

Angle of refraction: The angle between the refracted ray and the normal.

Angle of repose: The angle of inclination of a plane with the horizontal such that a body placed on the plane is at the verge of sliding.

Angstrom: A unit of length, 1 = 10-10 m.

Angular momentum: Also called moment of momentum, it is the cross product of position vector and momentum.

Angular velocity: The rate of change of angular displacement with time.

Annihilation: A process in which a particle and antiparticle combine and release their rest energies in other particles.

Antineutrino: The antiparticle of neutrino, it has zero mass and spin ½.

Archimedes principle: A body immersed in a fluid experiences an apparent loss in weight which is equal to the weight of the fluid displaced by the body.

Atomic mass unit: It is equal to one-twelfth the mass of C -12 isotope of carbon, 1 amu = 1.66x 10-27 Kg.

Atomic number: The number of protons in an atomic nucleus.

Avogadro number: The number of molecules in a gram molecular weight of a substance, it is equal to 6.02 x 1023.
Avogadro's law: Under the same conditions of temperature and pressure, equal volumes of all gases contain equal number of molecules.:-)