Physics Dictionary (Contd...)

Atmospheric Electricity
The conductivity of atmosphere arises from ions created by cosmic rays. The conductivity is variable; as we go to higher altitudes, conductivity gradually increases and at about 50km, atmosphere is pretty good conductor. This electrical phenomenon takes place between two conducting spherical surfaces, earth and top of stratosphere. Each of these surfaces is equipotential.

Atmospheric Pressure
The atmospheric air exerts normal pressure upon all surfaces with which it is in contact, and is known as atmospheric pressure.

Atom Bomb
Nuclear weapon which harnesses the forces that hold the nucleus of an atom together, by using the energy released when the nucleus splits into nucleons. The atom bomb works on principle of nuclear fission. Nuclear reactions occur when neutrons are fired at closely packed atoms with heavy fissile nuclei like uranium-235 / Plutonium isotopes. This leads to nuclear fission which further converts to chain reaction.

Atom Percent (at %)
It is defined as concentration specification on basis of number of moles (or atoms) of a particular element relative to the total number of moles (or atoms) of all elements within an alloy.

Atom
It is tiny basic unit of matter which is neutral and from which any substance gets constructed. It has positively charged nucleus constituting nucleons (Protons & Neutrons) surrounded by electrons revolving round the nucleus.  

Atomic Clock
It is accurate type of time device in the world, which is controlled by vibrations of an atomic or molecular system such as Cesium or Ammonia. The precision of an atomic clock depends on fact that an atom, caused to oscillate, will always vibrate at same frequency. NIST-F1, the United States standard atomic clock, is said to be so accurate that it would neither gain nor lose a second in over 30 yrs. They are used as primary standard in global navigation satellite system such as GPS.

Atomic Mass Unit (amu)
It is defined as 1/12 of mass of Carbon-12 atom. It is average of Proton & Neutron rest mass i.e. 1.67377 x 10-24 gm. The unit is used to express relative masses of various isotopes of element.

Atomic Number
The number of protons found inside the nucleus of a particular atom. The modern periodic table is structured based on this number.

Atomic Orbital
A quantum state attributed to electron around atom in quantum mechanics to describe wave characteristic of electron.  It is expressed by mathematical function which is used to calculate probability of finding any electron in any specific region around atom’s nucleus.

Atomic Packing Fraction
It is the ratio of volume of atoms per unit cell to volume of unit cell in a crystal structure.

Atomic Physics
It is study of structure of atom, arrangement of electrons around nucleus i.e. energy states, interaction of atoms with other particles and with electric and magnetic fields.

Atomic Radius
It is defined as half the distance between neighboring atoms in a crystal of a pure element.

Atomic Structure
It is study of configuration of atom which is essential for knowing many phenomenon involving electrons. Bohr’s atomic model is early model which has explained structure of atom to a great extent. Later the limitations of that model overcome by attributing dual nature to particle. The atomic structure represents the manner in which electron states are occupied.

Atomic Weight
It is the weighted average of the atomic masses of an atom’s naturally occurring isotopes. It is usually expressed in amu.

Atomicity
Total no. of atoms present in one molecule of an element of a substance is called as atomicity.

Atto
Prefix in metric system denoting a factor of 10-18.

Audio Frequency
It is the frequency range of periodic vibrations audible to human ear. The range is 20Hz to 20 KHz.

Audio Meter
It is an instrument for measuring hearing activity for pure tones of normally audible frequencies. 

Aufbau’s Principle
Principle which states that sub-shell of lower energy in an atom is filled up first while that of higher energy is filled up later.

Auger Effect
See Auger electron.

Auger Electron

In photoelectric effect, following expulsion of photoelectron, another electron from high energy state may occupy its location emitting X-ray photon. This photon may in turn eject electron from loosely bound outer electron shell, called auger electron and such photoelectric effect is called “Auger Effect”.

Physics Dictionary (Contd...)

Atmospheric Electricity
The conductivity of atmosphere arises from ions created by cosmic rays. The conductivity is variable; as we go to higher altitudes, conductivity gradually increases and at about 50km, atmosphere is pretty good conductor. This electrical phenomenon takes place between two conducting spherical surfaces, earth and top of stratosphere. Each of these surfaces is equipotential.

Atmospheric Pressure
The atmospheric air exerts normal pressure upon all surfaces with which it is in contact, and is known as atmospheric pressure.

Atom Bomb
Nuclear weapon which harnesses the forces that hold the nucleus of an atom together, by using the energy released when the nucleus splits into nucleons. The atom bomb works on principle of nuclear fission. Nuclear reactions occur when neutrons are fired at closely packed atoms with heavy fissile nuclei like uranium-235 / Plutonium isotopes. This leads to nuclear fission which further converts to chain reaction.

Atom Percent (at %)
It is defined as concentration specification on basis of number of moles (or atoms) of a particular element relative to the total number of moles (or atoms) of all elements within an alloy.

Atom
It is tiny basic unit of matter which is neutral and from which any substance gets constructed. It has positively charged nucleus constituting nucleons (Protons & Neutrons) surrounded by electrons revolving round the nucleus.  

Atomic Clock
It is accurate type of time device in the world, which is controlled by vibrations of an atomic or molecular system such as Cesium or Ammonia. The precision of an atomic clock depends on fact that an atom, caused to oscillate, will always vibrate at same frequency. NIST-F1, the United States standard atomic clock, is said to be so accurate that it would neither gain nor lose a second in over 30 yrs. They are used as primary standard in global navigation satellite system such as GPS.

Atomic Mass Unit (amu)
It is defined as 1/12 of mass of Carbon-12 atom. It is average of Proton & Neutron rest mass i.e. 1.67377 x 10-24 gm. The unit is used to express relative masses of various isotopes of element.

Atomic Number
The number of protons found inside the nucleus of a particular atom. The modern periodic table is structured based on this number.

Atomic Orbital
A quantum state attributed to electron around atom in quantum mechanics to describe wave characteristic of electron.  It is expressed by mathematical function which is used to calculate probability of finding any electron in any specific region around atom’s nucleus.

Atomic Packing Fraction
It is the ratio of volume of atoms per unit cell to volume of unit cell in a crystal structure.

Atomic Physics
It is study of structure of atom, arrangement of electrons around nucleus i.e. energy states, interaction of atoms with other particles and with electric and magnetic fields.

Atomic Radius
It is defined as half the distance between neighboring atoms in a crystal of a pure element.

Atomic Structure
It is study of configuration of atom which is essential for knowing many phenomenon involving electrons. Bohr’s atomic model is early model which has explained structure of atom to a great extent. Later the limitations of that model overcome by attributing dual nature to particle. The atomic structure represents the manner in which electron states are occupied.

Atomic Weight
It is the weighted average of the atomic masses of an atom’s naturally occurring isotopes. It is usually expressed in amu.

Atomicity
Total no. of atoms present in one molecule of an element of a substance is called as atomicity.

Atto
Prefix in metric system denoting a factor of 10-18.

Audio Frequency
It is the frequency range of periodic vibrations audible to human ear. The range is 20Hz to 20 KHz.

Audio Meter
It is an instrument for measuring hearing activity for pure tones of normally audible frequencies. 

Aufbau’s Principle
Principle which states that sub-shell of lower energy in an atom is filled up first while that of higher energy is filled up later.

Auger Effect
See Auger electron.

Auger Electron
In photoelectric effect, following expulsion of photoelectron, another electron from high energy state may occupy its location emitting X-ray photon. This photon may in turn eject electron from loosely bound outer electron shell, called auger electron and such photoelectric effect is called “Auger Effect”.

Physics Dictionary (Contd...)

Anti Logarithm
 If ‘y’ is result of logarithm of a given number ‘x’ then ‘x’ is antilog of ‘y’.

Anti Matter
Matter which comprises of antiparticles.

Anti Particle
Every fundamental particle is presumed to have an antiparticle which has same mass but opposite charge.

Anti-Node
Position of particles on a wave which vibrate simple harmonically with maximum amplitude is called anti node.

Antistokes Lines
The smaller frequency lines in Raman spectra are called Anti-Stokes lines.

Aphelion
The point in the orbit of planet, at which it is farthest from sun, is termed as Aphelion.

Aperture
Word attributed to small opening in an optical system or arrangement or instrument, through which light is made to pass for focusing it on to any plane.

Aplanatic Points
See Aplanatism

Aplanatism
The property of the surface by virtue of which all rays starting from a particular point object on its axis, after reflection or refraction at the surface, converge or appear to diverge from a single point image, is called aplanatism and the particular object and image points are called aplanatic points while the surface is said to be aplanatic surface with respect to those two points. 

Apochromat
A term applied to photographic & microscope objectives indicating highest degree of color correction.

Apogee
Point at which a satellite or any object orbiting earth is farthest from center of earth. At its apogee, object travels slower than at any other point in orbit.

Arc
The arc refers to the set of points on a circle that lie in the interior of circle. The arc can be any part of circumference.                                                                                            
or
The arc is a closed segment of a differentiable curve in the 2D plane.

Archimedes Principle
As per this principle when a body is fully or partially submerged in a fluid, a buoyant force from the surrounding fluid acts on the body. The force is directed upward and has a magnitude equal to weight on fluid that has been displaced by body.

Area
It is mathematical quantity that describes the amount of space extended by two dimensional surface area in the plane.

Artificial Transmutation
An artificially induced nuclear reaction caused by the bombardment of a nucleus with subatomic particles or small nuclei. The phenomenon was first observed and proposed by Ernest Rutherford.

Asteroids
They are small, rocky objects revolving around the sun that are too small to be called planets. They are also called Planetoids.

Astigmatism
Defect in optical system where rays that propagate in two perpendicular planes have different foci. It is a vision condition that causes blurred vision either due to the irregular shape of cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye. An irregular shaped cornea or lens prevents light from focusing properly on the retina, the light sensitive surface at the back of the eye. As a result,  vision becomes blurred at any distance.

Astronaut
A person who is trained to pilot, navigate, or otherwise participate as a crew member of a space craft is known as Astronaut.

Astronomical Unit (au)
An astronomical unit is approximately mean distance between Earth and Sun. It is a derived constant and used to indicate distances with in solar system. Symbol au is recommended by international astronomical union.
1a.u. = 149,597,870.691 KM

Astronomy
It is the Branch of science which deals with study of universe comprising celestial objects such as planets, stars etc. outside earth atmosphere. The study covers evolution, composition, motion, etc of universe.

Astrophysics
The branch of astronomy that deals with the physical and chemical processes that occur in stars, galaxies and interstellar space is called Astrophysics. Astrophysics deals with structure & evolution of stars, properties of interstellar space and its interaction with system of stars, and with structure and dynamics of cluster of stars such as galaxies.

Athermanous
Substances opaque to the thermal radiation are called athermanous.

Atmosphere
The mixture of gases surrounding the earth or other celestial body, held in place by gravity is referred to as atmosphere. It forms five distinct layers at different heights. The earth’s atmosphere consists in ascending order, the Troposphere (containing 90% of the atmosphere mass), the Stratosphere, the Mesosphere, the Thermosphere and Exosphere. Atmosphere is composed primarily of Nitrogen (78%), Oxygen (21%) and plays major role in water cycle, Nitrogen cycle & Carbon cycle.   

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.

ELECTROMAGNETIC SPECTRUM DETAILS

GAMMA RAYS


Wavelength range: 10-14 to 10-10  meter
 Frequency range: 3x1018 to 3 x 1022 Hz
Production: Nuclear origin. Emitted on disintegration of Nuclei of atoms.
Properties: Highly penetrating and uncharged. Exhibits Fluorescence, Phosphorescence, ionization and chemical reaction on photographic plates.
Uses: gives information about structure of nuclei.
X-rays


Wavelength range: 10-10 to 10-8  meter
 Frequency range: 3x1016 to 3 x 1018 Hz
Production: by striking high speed electrons on heavy target.
Properties: All properties of gamma rays but less penetrating.
Uses: helpful in medical diagnosis, study of crystal structure.
U V REGION


Wavelength range: 10-8 to 4x10-7  meter
 Frequency range: 8x1014 to 3 x 1016 Hz
Production: by sun, arc, spark and ionized gases.
Properties: All properties of gamma rays but less penetrating. They can produce photoelectric effect.
Uses: used in medical applications. Detection of finger prints, forged documents.
VISIBLE


Wavelength range: 4x10-7 to 7.8x10-7  meter
 Frequency range: 4x1014 to 8 x 1014 Hz
Production: radiated from ionized gases and incandescent bodies.
Properties: exhibit reflection, refraction, interference, diffraction, polarization, photoelectric effect, sensation of sight.
Uses: used in LASER technology.
INFRARED


Wavelength range: 7.8x10-7 to 10-3  meter
 Frequency range: 3x1011 to 4 x 1014 Hz
Production: by hot bodies
Properties: heating effect on thermo piles and bolometer. Exhibit reflection, refraction, diffraction and photographic action.
Uses: used in industry, astronomy & medicine etc.
HERTZIAN WAVES/ MICROWAVES

Wavelength range: 10-3 to 1 meter.
 Frequency range: 109 to 3 x 1011 Hz
Production: by spark discharge, by electronic devices such as Klystron & Magnetron.
Properties: Reflection, Refraction & Diffraction. Produces spark in gaps and receiving circuits.
Uses: used in Radar and MASERs and also to reveal finer details of atomic and molecular structure.
RADIO WAVES

Wavelength range: 1 TO 104 meter.
Frequency range: 10 KHz to 30 GHz
Production: oscillating circuits and electronic devices.
Properties: exhibits Reflection, Refraction & Diffraction.
Uses: used in television and radio broadcast system.

How does mass depend on speed?


In order to answer this question, we have to consider two situations:

a) The object could be at rest in our reference frame.

b) The "object" is never at rest in any (physically realizable) frame of reference.

An electron and a tennis ball belong to situation (a), where as a photon belongs to situation (b)

Let us assume that two masses exist, the mass when object has zero speed 'm0' and mass 'm' when object has speed 'V' as observed in our frame of reference.

When the object has zero speed, it is at rest (as observed by us or by someone accompanying the object), and so 'm0' is called the object's rest mass. It is an intrinsic property of the object.

For instance every electron has rest mass m0=9.11 x 10^-31 Kg.

If we set into motion a tennis ball that is initially at rest, the ball acquires kinetic energy, the energy associated with motion.Its energy increases.

From the equation  E=mC2; it implies that increase in energy will correspond to increase in mass too. We deduce that ball's inertia increases. Thus the mass 'm' of moving ball is greater than the rest mass 'm0'. Hence m>m0 holds for any object with kinetic energy.

In 1905, Einstein summarized his theoretical discovery with sentence,

" The mass (i.e. the inertia) of a body is a measure of its energy content.