ISTILAH DALAM FISIKA

(TERM IN PHYSICS)

Absolute humidity: The ratio of water vapor in a sample of air to the volume of the sample.

Absolute zero: The temperature of - 273.16 or 0 K at which molecular motion vanishes.

Absorptance: The ratio of the total absorbed radiation to the total incident radiation.

Acceleration: The rate of change of velocity with respect to time.

Acceleration due to gravity: The acceleration imparted to bodies by the attractive force of the earth or any other heavenly body.

Achromatic: capable of transmitting light without decomposing it into its constituent colors.

Acoustics: The science of the production, transmission and effects of sound.

Acoustic shielding: A sound barrier that prevents the transmission of acoustic energy.

 Adiabatic: Any change in which there is no gain or loss of heat.

Afocal lens: A lens of zero convergent power, whose focal points are infinitely distant.

Albedo: The fraction of the total light incident on a reflecting surface, especially a celestial body, which is reflected back in all directions.

Alpha particle: The nucleus of a helium atom (two protons and two neutrons) emitted as radiation from a decaying heavy nucleus.

Alternating current: The electric current that changes its direction periodically.

Amorphous: Solids which have neither definite form nor structure.

Ampere: S.I. Unit of electric current, one ampere is the flow of one coulomb of charge per second.

Amplitude: The maximum absolute value attained by the disturbance of a wave or by any quantity that varies periodically.

Angle of contact: 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: The angle between the incident ray and the normal.

Angle of reflection: The angle between the reflected ray and the normal.

 Angle of refraction: The angle between the refracted ray and the normal.

 Angle of repose: 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: A unit of length, 1 = 10-10 m.

Angular momentum: Also called moment of momentum, it is the cross product of position vector and momentum.

 Angular velocity: The rate of change of angular displacement with time.

Annihilation: A process in which a particle and antiparticle combine and release their rest energies in other particles.

Antineutrino: The antiparticle of neutrino, it has zero mass and spin ½.

Archimedes principle: 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: It is equal to one-twelfth the mass of C -12 isotope of carbon, 1 amu = 1.66x 10-27 Kg.

Atomic number: The number of protons in an atomic nucleus.

Avogadro number:The number of molecules in a gram molecular weight of a substance, it is equal to 6.02 x 1023.

Avogadro's law:Under the same conditions of temperature and pressure, equal volumes of all gases contain equal number of molecules.

Balmer lines: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:A unit of pressure, equal to 105 Pascals.

Baryon:subatomic particle composed of three quarks.

Beat:A phenomenon of the periodic variation in the intensity of sound due to superposition of waves differing slightly in frequency.

Bernoulli's theorem:The total energy per unit volume of a non-viscous, incompressible fluid in a streamline flow remains constant.

Beta particle:An electron emitted from a nucleus in radioactive decay.

 Binding energy:The net energy required to decompose a system into its constituent particles.

Black body:An ideal body which would absorb all incident radiation and reflect none.

Black hole:The remaining core of a supernova that is so dense that even light cannot escape.

Boyle's law:For a given mass of a gas at constant temperature, the volume of the gas is inversely proportional to the pressure.

Brewster's law:States that the refractive index of a material is equal to the tangent of the polarizing angle for the material.

Brownian motion: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:The ratio of normal stress to the volumetric strain produced in a body.

 Buoyant force:upward force on an object immersed in fluid.

Calorie:A unit of heat, 1Calorie = 4.186 joules.

Candela: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:The ratio of charge stored per increase in potential difference.

Capacitor:Electrical device used to store charge and energy in the electrical field.

Capillarity:The rise or fall of a liquid in a tube of very fine bore.

Carnot's theorem:No engine operating between two temperatures can be more efficient than a reversible engine working between the same two temperatures.

Centrifugal force:An outward pseudo force acting on a body in circular motion.

Centripetal force:The radial force required to keep an object moving in a circular path; it is equal to mv2/r.

Charles' law:For a given mass of a gas at constant pressure, the volume is directly proportional to the temperature.

Chromatic aberration: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: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:The system which cannot exchange heat or matter with the surroundings.

Coefficient of linear expansion:The increase in length per unit original length per degree rise in temperature.

Coefficient of superficial expansion:The increase in area per unit original area per degree rise in temperature.

Coefficient of volumetric expansion:The increase in volume per unit original volume per degree rise in temperature.

Coherent source:A source in which there is a constant phase difference between waves emitted from different parts of the source.

Condensation point:The temperature at which a gas or vapor changes back to liquid.

Conduction: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:The transfer of heat by the actual transfer of matter.

Coulomb's law: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:The angle of incidence in a denser medium for which angle of refraction is .

Cyclotron:A device used to accelerate the charged particles.

 

Decibel: 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: The mass of a substance per unit volume. Diffraction: The bending of light around the corners of an object. Dioptre: Unit of power of a lens. Direct current: An electrical current which always flows in one direction. Dispersion: The splitting of white light into its component colors. Displacement: The shortest distance between the initial and final position of a moving body. It is a vector quantity. Distance: The actual path length covered by a body. It is a scalar quantity. Doppler Effect: The apparent change in the frequency of a wave due to relative motion between the source and the observer.

Einstein mass energy relation: E = mc2, E is the energy released, m is the mass defect and c is the speed of light.

Electric current: The rate of flow of electric charge.

Electric field line: An imaginary curve tangent to which at a point gives the direction of electric field at that point.

Electric potential energy: The energy due to the position of a charge near other charges. Electrical conductors: The materials that have free electrons and allow current to flow through them.

Electrical insulators:The materials which do not allow current to flow through them.

Electrical resistance:The property to oppose the flow of current.

Electromagnetic induction:The process in which current is induced in a coil whenever there is a change in the magnetic flux linked with the coil.

Electron volt:The energy gained by an electron when it passes through a potential difference of one volt, it is equal to 1.60 x 10-19 Joules.

Endothermic process:The process in which heat is absorbed.

 Exothermic process:The process in which heat is evolved.

Escape Velocity:The minimum velocity with which an object must be thrown upwards so as to overcome the gravitational pull, it is equal to , where M is the mass of the planet and R is the radius of the planet.