Alternating current (ac) - current in which electrons oscillate instead of moving with same drift speed in the same direction

Alternating voltage - voltage that takes positive as well as negative values

Ammeter - an instrument that measures the electric current through it

Amplitude - the largest value of the displacement from equilibrium of an oscillation

Angular frequency - same as angular speed

 - the product of mass, speed and orbit radius of a particle

Angular separation - the angle that the distance between two objects subtends at the observer’s eye

Angular speed - the ratio of angle turned to time taken

Aniontons’ law or Gay-Lussac’s law - the relation between pressure and temperature of a fixed quantity of an ideal gas when the volume is kept constant

Anti-particle - a particle with the same mass as its particle but with all other properties opposite, such as electric charge