Ammeter Device used to measure current. It is designed with a small resistance put in parallel to the galvanometer. It is generally connected in series with in a circuit, in which electric resistance is to be measured. Amorphous Materials that do not crystallize, i.e. in which, long range atomic order is absent, are referred to as amorphous.          Ampere It is the constant current which if maintained in two straight parallel conductors of infinite length and of negligible cross-section and placed one meter apart in vacuum, would produce between these conductors a force equal to 2 x 10-7 N/M of length.   Amperes Law A law of electromagnetism which expresses contribution of a current element of length dl to the magnetic induction ‘B’ at a point near the current carrying element. The law was derived by A M Ampere. Whenever an electric charge is in motion, there is magnetic field associated with that motion. The flow of charges through a conductor sets up magnetic field in the surrounding region. Any current may be considered to be broken up into infitesimal elements of length dl and each such element contributes to magnetic induction at every point in neighborhood. The contribution dB of the element is found to depend upon current I, the length dl of element, distance ‘r’ of point ‘p’ from current element, and angle ‘Ѳ’ between current element and line joining point ‘p’.               dB=  (KldIsinѲ/r2);  K = µo/4Π = 10-7 Weber/Ampere-meter   Amplifier Device used for increasing the strength of a weak signal. Amplitude Modulation The process of changing the amplitude of high frequency carrier wave in accordance with intensity of signal without changing frequency, is called amplitude modulation. Amplitude The maximum displacement of a vibrating particle in simple harmonic motion is called as amplitude.  Analog Analog is defined as a mechanism in which data is represented by continuously variable physical quantities.     Anelasticity In some engineering materials, there also exists time dependent elastic strain component. That is elastic deformation will continue even after stress application and upon load release, some finite time is required for complete recovery. This time dependant elastic behavior is known as anelasticity.   Anemometer The term is derived from Greek word “anemos”, meaning wind. It is device used for measuring speed of air flow in wind tunnels, and in other gas flow applications. Angle The amount of space between two straight lines having a common end point usually measured in degrees. Angle of Incidence Angle between incidence ray and normal to the surface is called angle of incidence. Angle of Minimum Deviation When the angle of incidence in a prism is increased, the value of angle of deviation first decreases and then increases. The minimum value of deviation is called the angle of deviation. Angle of Reflection It is the angle between reflected ray and normal to the surface, from which light is reflected. Angle of Refraction It is the angle between refracted ray and the surface from which light is refracted. Angstrom It is the unit of length usually used to express sizes at atomic scale. It is equal to 10-10 meter. Angular Acceleration It is defined as the rate of change of angular velocity. Angular Aperture Angular aperture of an objective is largest angular extent of wave surface which it can transmit. Angular Displacement When a particle describes circular path, the angle described by the radius vector in a given time interval is called angular displacement. Its direction is perpendicular to plane of rotation along the axis.