Dictionary of Physics
By Students’ Academy
Copyright@2011Students’ Academy
Smashwords Edition
Chapter 1: A
Absolute Humidity
Absolute Humidity refers to the ratio of water vapor in a sample of air to the volume of the sample.
Absolute zero
Absolute Zero is the temperature of 273.16 or 0 K at which molecular motion vanishes.
Absorptance
Absorptance refers to the ratio of the total absorbed radiation to the total incident radiation.
Acceleration
Acceleration is the rate of change of velocity with respect to time.
Acceleration due to gravity
Acceleration due to gravity is the acceleration which is imparted to bodies by the attractive force of the earth or any other heavenly body.
Achromatic
Achromatic refers to the state of being capable of transmitting light without decomposing it into its constituent colors.
Acoustics
Acoustics is the science of the production, transmission and effects of sound.
Acoustic shielding
Acoustic Shielding is a sound barrier that prevents the transmission of acoustic energy.
Adiabatic
Adiabatic refers to any kind of a change in which there is no gain or loss of heat.
Afocal lens
Afocal lens is the lens of zero convergent power, whose focal points are infinitely distant.
Albedo
Albedo is the fraction of the total light incident on a reflecting surface, especially a celestial body, which is reflected back in all directions.
Alpha particle
Alpha Particle is the nucleus of a helium atom (two protons and two neutrons) emitted as radiation from a decaying heavy nucleus.
Alternating current
Alternating current is the electric current which changes its direction periodically.
Amorphous
Amorphous refers to the solids which have neither definite form nor structure.
Ampere
Ampere is the S.I. Unit of electric current, one ampere is the flow of one coulomb of charge per second.
Amplitude
Amplitude is the maximum absolute value attained by the disturbance of a wave or by any quantity that varies periodically.
Angle of contact
Angle of Contact is the angle between tangents to the liquid surface and the solid surface inside the liquid, both the tangents drawn at the point of contact.
Angle of incidence
Angle of Incidence refers to the angle between the incident ray and the normal.
Angle of reflection
Angle of Reflection refers to the angle between the reflected ray and the normal.
Angle of refraction
Angle of Refraction refers to the angle between the refracted ray and the normal.
Angle of repose
Angle of Repose refers to the angle of inclination of a plane with the horizontal such that a body placed on the plane is at the verge of sliding.
Angstrom
Angstrom is the unit of length, 1 = 10-10 m.
Angular momentum
Angular Momentum is also called moment of momentum, it is the cross product of position vector and momentum.
Angular velocity
Angular Velocity is the rate of change of angular displacement with time.
Annihilation
Annihilation is a process in which a particle and antiparticle combine and release their rest energies in other particles.
Antineutrino
Antineutrino is an antiparticle of neutrino, it has zero mass and spin ½.
Archimedes principle
Archimedes Principle proves that a body immersed in a fluid experiences an apparent loss in weight which is equal to the weight of the fluid displaced by the body.
Atomic mass unit
Atomic Mass Unit is equal to one-twelfth the mass of C -12 isotope of carbon, 1 amu = 1.66x 10-27 Kg.
Atomic number
Atomic Number is the number of protons in an atomic nucleus.
Avogadro number
Avogadro Number is the number of molecules in a gram molecular weight of a substance, it is equal to 6.02 x 1023.
Avogadro's law
Avogadro’s Law shows that under the same conditions of temperature and pressure, equal volumes of all gases contain equal number of molecules.
Chapter 2: B
Balmer lines
Balmer Lines refer to the lines in the spectrum of hydrogen atom in visible range, produced by transition between n 2 and n = 2, n is the principal quantum no.
Bar
Bar is a unit of pressure, equal to 105 Pascals.
Baryon
Baryon is a subatomic particle composed of three quarks.
Beat
Beat is a phenomenon of the periodic variation in the intensity of sound due to superposition of waves differing slightly in frequency.
Bernoulli's theorem
Bernoulli’s Theorem proves that the total energy per unit volume of a non-viscous, incompressible fluid in a streamline flow remains constant.
Beta particle
Beta Particle is an electron emitted from a nucleus in radioactive decay.
Binding energy
Binding Energy refers to the net energy required to decompose a system into its constituent particles.
Black body
Black Body refers to an ideal body which would absorb all incident radiation and reflect none.
Black hole
Black Hole refers to the remaining core of a supernova that is so dense that even light cannot escape.
Boyle's law
Boyle’s Law says that a given mass of a gas at constant temperature, the volume of the gas is inversely proportional to the pressure.
Brewster's law
Brewster’s Law says that the refractive index of a material is equal to the tangent of the polarizing angle for the material.
Brownian motion
Brownian Motion refers to the continuous random motion of solid microscopic particles when suspended in a fluid medium due to the consequence of ongoing bombardment by atoms and molecules.
Bulk's modulus of elasticity
Bulk’s Modulus of Elasticity refers to the ratio of normal stress to the volumetric strain produced in a body.
Buoyant force
Buoyant Force refers to the upward force on an object immersed in fluid.
Chapter 3: C
Calorie
Calorie is a unit of heat, 1Calorie = 4.186 joules.
Candela
Candela is the S.I. unit of luminous intensity defined as the luminous intensity in a given direction of a source that emits monochromatic photons of frequency 540 x 1012 Hz & has a radiant intensity in that direction of 1/683 W/sr
Capacitance
Capacitance refers to the ratio of charge stored per increase in potential difference.
Capacitor
Capacitor is an electrical device which is used to store charge and energy in the electrical field.
Capillarity
Capillarity refers to the rise or fall of a liquid in a tube of very fine bore.
Carnot's theorem
Carnot’s Theorem says that no engine operating between two temperatures can be more efficient than a reversible engine working between the same two temperatures.
Centrifugal force
Centrifugal Force is the outward pseudo force acting on a body in circular motion.
Centripetal force
Centripetal Force is the radial force required to keep an object moving in a circular path; it is equal to mv2/r.
Charles' law
Charles’ Law states that for a given mass of a gas at constant pressure, the volume is directly proportional to the temperature.
Chromatic aberration
Chromatic Aberration is an optical lens defect causing color fringes, because the lens brings different colors of light to focus at different points.
Clausius' statement of second law of Thermodynamics
Clausius’ statement of second law of thermodynamics states that it is not possible that at the end of a cycle of changes heat has been transferred from a colder body to a hotter body without producing some other effect.
Closed system
Closed System is the system which cannot exchange heat or matter with the surroundings.
Coefficient of linear expansion
Coefficient of Linear Expansion refers to the increase in length per unit original length per degree rise in temperature.
Coefficient of superficial expansion
Coefficient of Superficial Expansion refers to the increase in area per unit original area per degree rise in temperature.
Coefficient of volumetric expansion
Coefficient of Volumetric Expansion refers to the increase in volume per unit original volume per degree rise in temperature.
Coherent source
Coherent Source is the source in which there is a constant phase difference between waves emitted from different parts of the source.
Condensation point
Condensation Point refers to the particular temperature at which a gas or vapor changes back to liquid.
Conduction
Conduction refers to the transfer of heat from a region of higher temperature to a region of lower temperature by increased kinetic energy moving from molecule to molecule.
Convection
Convection refers to the transfer of heat by the actual transfer of matter.
Coulomb's law
Coulomb’s Law states that the force between any two charges is directly proportional to the product of charges and inversely proportional to the square of the distance between the charges.
Critical angle
Critical Angle refers to the angle of incidence in a denser medium for which angle of refraction is .
Cyclotron
Cyclotron is a device which is used to accelerate the charged particles.
Chapter 4: D
Decibel
Decibel is the unit of sound level, if P1 & P2 are two amounts of power, the first is said to be n decibels greater, where n = 10 log10 (P1/P2)
Density
Density is the mass of a substance per unit volume.
Diffraction
Diffraction refers to the bending of light around the corners of an object.
Dioptre
Dioptre is the unit of power of a lens.
Direct current
Direct Current is an electrical current which always flows in one direction.
Dispersion
Dispersion refers to the splitting of white light into its component colors.
Displacement
Displacement refers to the shortest distance between the initial and final position of a moving body. It is a vector quantity.
Distance
Distance is the actual path length covered by a body. It is a scalar quantity.
Doppler Effect
Doppler Effect refers to an apparent change in the frequency of a wave due to relative motion between the source and the observer.