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Physics Definitions Start from A

Absolute Zero - The lowest possible temperature in the universe, at which all atomic activity ceases. Equal to -273 degrees Celsius (- 459 degrees Fahrenheit). Used as a benchmark for measuring temperature.

Accelerator - A machine that serves as a source for a well-defined beam of high speed particles for studies in nuclear science and high energy (or particle) physics.

Angstrom - Abbreviated Ň. A unit of length equal to 10-8 cm (one-hundredth of a millionth of a centimeter). An Angstrom is on the order of the size of an atom.

Antiparticle - A metal that when cooled below a critical temperature has a total disappearance of electrical resistance. Twenty-five elements and many alloys and compounds have been found to be superconducting. The critical temperatures range from .002 k to 18K

Arc Degree - A unit of angular measure in which there are 360 arc degrees in a full circle.

Arc Second - Abbreviated arcsec. A unit of angular measure in which there are 60 arc seconds in 1 arc minute and therefore 3600 arc seconds in 1 arc degree. One arc second is equal to about 725 km on the Sun.

Atom - A point-like particle with a negative charge; member of the lepton group and thus not divisible into more fundamental particles.

Accuracy - Closeness of a measurement to the standard value of that quantity.

Achromatic Lens - Lens for which all light colors have the same focal length.

Action-Reaction Forces - Pair of forces involved in an interaction that are equal in magnitude and opposition in direction.

Activity - Number of decays per second of a radioactive substance.

Adhesion - Force of attraction between two unlike materials.

Air Resistance - Force of air on objects moving through it.

Alpha Decay - Process in which a nucleus emits an alpha particle.

Alpha Particle - Positively- charged particles consisting of two protons and two neutrons emitted by radioactive materials.

Ammeter - Device to measure electrical current.

Amorphous solid - Solids that have no long range order; no crystal structure.

Ampere - Unit of electric current; one ampere is the flow of one coulomb of charge per second.

Amplitude - In any periodic motion, the maximum displacement from equilibrium.

Angle of Incidence - Angle between direction of motion of waves and a line perpendicular to surface the waves are striking.

Angle of Reflection - Angle between direction of motion of waves and a line perpendicular to surface the waves are reflected from.

Angle of Refraction - Angle between direction of motion of waves and a line perpendicular to surface the waves have been refracted from.

Angular Momentum - Quantity of rotational motion. For a rotating object, product of moment of inertia and angular velocity.

Annihilation - Process in which a particle and its antiparticle are converted into energy.

Antenna - Device used to receive or transmit electromagnetic waves.

Antineutrino - Subatomic particle with no charge or mass emitted in beta decay.

Antinode - Point of maximum displacement of two superimposed waves.

Archimedes’ Principle - Object immersed in a fluid has an upward force equal to the weight of the fluid displaced by the object.

Artificial Radioactivity - Radioactive isotope not found in nature.

Atomic mass unit - Unit of mass equal to 1/12 the atomic mass of carbon- 12 nucleus.

Atomic number - Number of protons in the nucleus of the atom.

Average Acceleration - Acceleration measured over a finite time interval

Average velocity - Velocity measured over a finite time interval.

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