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### Physics Dictionary (Contd...)

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.    ther particles and with electric and magnetic fi

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.

Angular Momentum
It is the ability of a body by virtue of which it imparts rotatory motion to other bodies. Angular momentum is product of linear momentum and perpendicular distance of direction of linear momentum from center of rotation.

Angular velocity
It is defined as rate of change of angular displacement.

Anisotropy
It is the phenomenon of exhibiting different values of a physical property in different crystallographic directions.

Annealing
It is the process of heat treatment of metal by which microstructure and consequently properties of a material are altered. Annealing is generally heating of metal to specific temperature, for certain duration and then allowed to cool slowly thus softening by re-crystallizing. Cold worked metals usually undergo this for relieving strain.

Anode Rays
Rays of positively charged particles formed inside gas discharge tubes. These rays were discovered by Goldstein in 1886.

Anode
It is the electrode in an electrochemical cell that experiences oxidation, or gives up electron.

Anodizing
It is an electrochemical metal finishing process used for increasing thickness and toughness of the naturally occurring protective oxides on surface of metals. The process is called anodizing, as the part to be chemically treated forms the anode electrode of electric circuit. The process increases non-corrosiveness & non-conductivity.

Anomalous Dielectric Dispersion
The fall in permittivity of a dielectric material with increasing frequency of external electric field is a phenomenon called anomalous dielectric dispersion.

Anomalous Expansion of Water
When temperature of water is raised from 0 oC, its volume decreases up to 4 oC and above 4 oC its volume increases. This is called anomalous expansion. It is due to formation of more number of Hydrogen bonds.

Anomalous Zeeman Effect
When spectral lines of an atom split into three or more unequally spaced lines in the presence of magnetic field then the phenomenon is called as anomalous Zeeman effect. This usually happens for the systems where net spin i.e. spin quantum number is not zero.

Antenna
A type of transducer that converts RF fields into alternating current or vice versa. A receiving antenna intercepts RF energy and delivers oscillating electric current to electronic equipment, and the transmitting antenna is fed with electric current to generate RF field. They consist of metallic conductors, electrically connected to transistor or receiver.

Anti Ferromagnetism

Phenomenon of magnetic moment (spin moments) of neighboring atoms or ions aligned in exactly opposite directions.