Aberrations - the failure of a lens to give a perfect image

Absicissa - horizontal axis of a graph

Absolute zero - the lowest theoretical temperature

Acceleration - the rate of change of velocity with respect to time

Acceleration of gravity - the acceleration of a mass with gravitational attraction as the only unbalanced force, usually denoted by "g"

Accommodation - change in the eye to keep an image in focus on the retina

Active medium - a material containing atoms or molecules that can be stimulated to emit light

Activity - the number of radioactive disintegration per unit time

Additive primary colors - red, green, and blue

Adiabatic process - a process during which no heat enters or leaves the system

Allowed bands - electronic energy states which are grouped by the effect of the periodic crystal potential

alpha rays - radioactivity composed of doubly charged helium ions

Alternating current – current resulting from a periodically varying voltage source

Ammeter – an instrument that measures the current passing through it

Amorphous solids – solids possessing only a short range order of atoms

Ampere – the SI unit of measurement for current

Ampère’s law – a relationship between the magnetic field around a current-carrying conductor and the current in the conductor (see equation 19.11)

Amplitude – maximum displacement from the equilibrium position, in periodic motion

Angle of incidence – the angle between the incoming ray and the normal (perpendicular to the surface)

Angle of reflection – the angle between the outgoing ray and the normal (perpendicular to the surface)

Angular magnification – the angle subtended by the image divided by the angle subtended by the object (see equation 23.2 and 23.3)

Angular momentum – the product of linear momentum and the distance from the mass to the axis of rotation

Angular velocity – the rate of change in the angle per unit time (see figure 5.7)

Antinode – in a standing wave pattern, a point that vibrates with the greatest amplitude, halfway between each pair of nodes

Antiparticles – the corresponding particle of the same mass but with the opposite charge

Antireflection coating – a thin film coating placed on a lens to minimize reflection from the surface of the lens

Archimedes’ principle – states that a body, whether completely or partially submerged in fluid, is buoyed upward by a force that is equal to the weight of the displaced fluid

Astigmatism – unevenness in the focusing of the eye

Average acceleration – change in velocity divided by the time required for the change

Average angular acceleration – change in angular velocity divided by the time required for the change

Average speed – the total distance traveled divided by the total time required for that travel

Average velocity – the displacement divided by the time elapsed during the displacement

Avogadro's number – the number of molecules in a mole of any substance