Physics Definitions Terminology Dictionary Glossary - Reference

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Absolute Zero or zero on the absolute temperature scale is the lowest temperature theoretically possible and is equal to -273.15°C or -459.67°F.

Physics Definitions Terminology Dictionary

Adiabatic process is a process in which no heat enters or leaves a system. An adiabatic expansion results in cooling of a gas whereas an adiabatic compression has the opposite effect.

Advection is a process of transfer of atmospheric properties by horizontal motion in the atmosphere.

Alpha Decay is a radioactive disintegration process in which the parent nucleus decays spontaneously into an alpha particle and a daughter nucleus.

Alpha particle is the nucleus of a helium atom carrying a positive charge of 2e.

Alternating current is an electric current that periodically reverses its direction in the circuit, with a frequency independent of the constants of the circuit.

Amplitude, is the peak value of an alternating quantity in either the positive or negative direction and is particularly applied to the case of a sinusoidal vibration.

Angstrom is the unit of wavelength of light. 1 Angstrom = 10-8 cm. There is a bigger unit for measuring the wavelength of infrared light; it is called a milli-micron and is equal to 10-7 cm. Micron = 10-4 cm, is a still bigger unit.

Angular displacement: The angle through which a point, line or body is rotated, in a specific direction and about a specified axis.

Angular velocity is the rate at which a body rotates about an axis, expressed in radians per second. It is a vector quantity equal to the linear velocity divided by the radius.

Anion is an ion that carries a negative charge and in electrolysis moves towards the anode.

Anode is the positive electrode of an electrolytic cell, discharge tube, valve or a rectifier.

Antenna is the term used in scientific and technical literature for "aerial". It was originally an American term.

Astigmatism refers to defect of an optical image in which the rays passing through the lens focus in different planes. It is caused due to unusual curvatures of cornea or aberration in the lens.

Atomic number is the number of protons contained in the nucleus of an atom or the number of electrons revolving around the nucleus.

Atomic energy is liberated by the disintegration of atom. Elements like uranium, etc., can be disintegrated to release atomic energy. 'The energy released in the fission of a single atom of uranium is about one million times the energy released per atom of the combustion of a fuel like coal.

Atomic pile is a nuclear chain reactor.

Atomic Volume is the volumes in the solid state of one mole of an element.

Atomic Weight is the weight of an atom of hydrogen taken as the standard; the respective weights of the atoms of all other substances arc expressed in terms of it. So, when it is stated that the atomic weight of iron is 56, it is meant that the atom of iron is 56 times as heavy as the atom of hydrogen.

Aurora is an intermittent electrical discharge occurring in the rarefied upper atmosphere.

Blackbody is the body whose surface absorbs all radiations incident on it and thus neither reflects nor transmits any radiation.

Boiling point is the temperature of a liquid at which visible evaporation occurs throughout the bulk of the liquid and at which the vapour pressure of the liquid equals the external atmospheric pressure. It is the temperature at which liquid and vapour can exist together in equilibrium at a given pressure.

Bomb Calorimeter is a device used for measuring the heat evolved by the combustion of a fuel.

Bond energy is the energy required to break a chemical bond between two atoms in a molecule. The bond energy depends on the type of atoms and on the nature of the molecule.

Boyle's law If a given mass of a gas is compressed at constant temperature the product of the pressure and volume remains' constant.

Breeder reactor is a nuclear reactor in which more fissile material is produced than is consumed.

Brownian movement is the unceasing and irregular motion of small particles (about 1 cm in diameter) when held in suspension in a liquid.

Buoyancy: Archimedes' principle states that if a body is wholly or partly immersed in a fluid, it experiences an upward force equal to the weight of the fluid which would fill the space occupied by the immersed part of the body.

Byte is a fixed number of "bits" (now almost always 8 bits) that can be handled and stored as a single unit in a computer.

Calibration is the determination of the absolute values of arbitrary indications of an instrument.

Calorie is the unit of heat. It is the amount of heat required to raise the temperature of one gram of water through 1°C.

Chain reaction is a series of nuclear transformations initiated by a single nuclear fission.

Charge is a property of some elementary, particles that causes them to exert force on one another.

Charles' Law (Also known as Gay-Lussac's Law): The volume of a fixed mass of any gas increases for each degree rise in temperature by - a constant fraction of the volume at 0°C to 100°C, the pressure being constant.

Critical temperature is the temperature above which a substance can exist only in its gaseous state and cannot be liquified regardless of the magnitude of pressure exerted on it. In metallurgy, it is the temperature at which a metal or alloy begins to change during heating or cooling.

Density is the mass pet unit volume of a substance. In SI units, it is measured in kg/m3.

Dew point is the highest temperature a surface may have in order that dew may condense on the surface from a humid atmosphere.

Dielectric is a substance that is capable of sustaining an electrical stress i.e. an insulator.

Diffusion is the process by which fluids and solids mix intimately with one another due to the kinetic motions of the particles.

Diode is any electronic device with only two electrodes. Diodes arc usually used as rectifiers.

Elasticity is the property of a body or substance by which it tends to resume its original size and shape after being subjected to deforming forces.

Electret is a piece of solid matter which retains a permanent electron polarisation like a permanent magnet.

Electrosmosis is the passage of an electrolyte through a membrane or porous partition under the influence of an electric current.

Emission is the liberation of electrons or electromagnetic radiations from the surface of a solid or liquid, usually electrons from a metal.

Equilibrium: A system of coplanar forces is in equilibrium when the algebraic sums of the resolved parts of the forces in any two directions are both zero and the algebraic sum of the moments of the forces about any point in their plane is zero.

Escape velocity is the velocity that ‘a projectile space probe etc., must reach in order' to escape the gravitational field of a planet or the moon. It depends on the mass and diameter of the planet. The escape velocity is about 11200 m/sec. for the Earth.

Fatigue is the progressive decrease of a property due to repeated stress.

Ferromagnetism is a property of certain solid substances that, having a large positive magnetic susceptibility, are capable of being magnetised by weak magnetic fields. The chief ferromagnetic elements are iron, cobalt and nickel.

Flash point is the lowest temperature at which a substance will provide sufficient inflammable vapour to ignite upon the application of a small flame.

Fluid is a collective term embracing liquids and gases.

Fluorescence is the absorption of radiant energy by a substance, immediately followed by its remission in the form of visible light of a greater wavelength.

Freezing mixture is a mixture of ice with salt so as to lower melting point of ice and keep other bodies cooler for longer time.

Fuse is a device to prevent unduly high current from passing through an electric circuit by breaking contact.

Fusion is the change of the state of a substance from solid to liquid which occurs at a definite temperature at a given applied pressure.

Gamma rays arc electromagnetic radiations emitted spontaneously by certain radioactive substances in the process of a nuclear transition.

Gauss's theorem is total electric flux acting normal to any closed surface drawn in an electric field is equal to the total charge of electricity inside the closed surface.

Generator is a machine for converting mechanical energy into electrical energy.

Heat exchanger is a device for transferring heat from one fluid to another without the fluids coming in contact. Its purpose is either to regulate the temperatures of the fluids for optimum efficiency of some process, or to make use of heat that would otherwise be wasted.

Hook-up is a temporary connection between electrical or electronic circuits or a temporary communications channel.

Horse Power is the practical unit of power—the power of an agent which can work at the rate of 550 foot-pounds per second or 33,000 foot-pounds per minute. MP = 746, watts.

Hypermetropia is a defect of eye in which near objects arc not distinctly visible. This is also called long-sightedness.

Ice point is the temperature of equilibrium of ice and water at standard pressure.

Incandescence is the emission of visible radiation from a substance at high temperature.

Incandescent lamp is an electric lamp in which light is produced by the heating effect of a filament of carbon, osmium or tungsten.

Incidence angle is the angle between the ray striking a reflecting or refracting surface and the normal to the surface at the point of incidence.

Inertia is property of matter by which it resists change in its state of rest or in its direction of motion.

Intensity is the rate of energy transfer per unit area normal to the direction of propagation at any given point.

Ion is electrically charged atom or group of atoms.

Isothermal is a line joining all points on a graph that correspond to the same temperature.

Isothermal process is a process that occurs at a constant temperature.

Isotopes arc atoms of an element having the same atomic number but different atomic weights.

Jet engine is aero-engine deriving its thrust from the high velocity of the gases it ejects.

Joule is the unit of work or energy. It is equal to 107 ergs. It is the energy consumed in one second in an electrical circuit through which a current energy of one ampere is flowing against a potential difference of one volt.

Joule's effect is the liberation of heat by the passage of a current through an electric conductor, due to its resistance.

Kilowatt-hour is a unit of energy equivalent to the energy produced when power of 1 kilowatt is expended for 1 hour.

Kinetic energy is the energy possessed by a particle or body by virtue of its motion.

Laminar flow is steady flow in which the fluid moves in parallel layers or laminae, the velocities of the fluid particles within each lamina not being necessarily equal.

Laser is a source of intense mono-chromatic coherent radiation in the visible, ultraviolet and infrared regions of the spectrum.

Latent heat is the quantity of heat required to convert 1 gm of a substance from one form into another. The unit is calories per grim.

Lightning is a disruptive discharge of electricity between a charged cloud and the earth or between two clouds. It is caused when the difference of potentials between a cloud and earth or between two clouds becomes so large that electricity passes across the gap.

Lightning conductor is a conductor of electricity installed in a structure to save it from damage. It neutralises the electric charge of the clouds coming in its contact or carries it to the earth.

Light Year is the distance light travels in one mean solar year, at the speed of 1,86,000 miles per second. It is equal to 5,880,000,000 miles. It is used as a unit for measuring stellar distances.

Magnetic circuit is the completely closed path described by a given set of lines of magnetic flux.

Magnetic field is the field, of force surrounding a magnetic pole or a current flowing through a conductor, in which there is a magnetic flux.

Mariner's Compass is an apparatus for determining direction, graduated to indicate 33 directions. The "N" point on the dial indicates north pole and the "S" point, south pole.

Mechanical equivalent of heat (Joule's Constant) is the ratio of amount of work done and the quantity of heat produced in a mechanical work. It is a constant.

Modulus of Elasticity is the ratio of stress to strain for a body obeying Hooke's law.

Molecular weight is the sum of the atomic weights of all the atoms contained in a molecule.

Momentum is the product of the mass and the velocity of the particle. It is a vector quantity directed through the particle in the direction of motion.

Myopia is a defect of vision blurring distant objects. Also called shortsightedness. It is corrected by the use of concave lenses.

Negative electron is an electron with a negative charge as opposed to the positively charged electron or positron.

Neutron is an elementary particle having zero charge and a rest mass of 1.674 x 10-27 kg, that is a constitute of the atomic nucleus.

Newton is the SI unit of force, defined as the force that provides a mass of one kilogramme with an acceleration of one metre per second per second.

Nuclear fission is splitting up of a heavy atom (e.g., uranium in two or more new atoms) with enormous release of energy.

Nuclear chain reaction occurs in radioactive elements charging the nuclei of atoms and yielding atoms of different elements or isotopes of the original elements.

Nucleon is the collective term for a "proton" or "neutron" i.e., for a constituent of an atomic nucleus.

Ohm is the SI unit of electrical resistance, defined as the resistance between two points on a conductor through which a current of one ampere flows as a result of a potential difference of one volt applied between the points, the conductor not being a source of electromagnetic force.

Ohm's Law states that the electric current in any conductor is proportional to the potential difference between its ends, other factors remaining constant.

Optical Centre is a point on the surface of a lens where the optical axis intersects the surface.

Paramagnetism is the property of substances that have a positive magnetic susceptibility.

Partial pressure is the pressure of a gas in a mixture of gases occupying a fixed volume of the pressure that the gas would exert if it has alone occupied the total volume.

Pascal's principle states that pressure applied at any point of a fluid at rest is transmitted without loss to all other parts of the fluid.

Pauli's Exclusion Principle is the principle that no two fermions can exist in identical quantum states, thus no two electrons in an atom can be identical in their quantum numbers.

Persistence of vision is the impression of an image on the retina for an instant after its withdrawal. Successive images produce an impression of continuity. The principle is used in cinema.

Presbyopia is a defect of vision in which objects are not clearly visible due to weakening of eye muscles in old age. It is overcome by the use of suitable lenses in the same frame.

Proton is a positive hydrogen ion; it is 1836 times heavier than electron.

Pyrometer is an instrument used for measuring high temperatures.

Quantum Theory is a theory which is based on Planck's radiation law. The concept of discontinuity of energy was introduced. According to this theory, changes of energy in atoms and molecules occur only in discrete quantities, each an integral multiple of a fundamental quantity. The fundamental quantity is generally referred to as quantum.

Quartz is a double refracting crystal, optically uniaxial and positive and rotating the plane of polarization to the left or right according to the variety, and to a different extent for different colours.

Radiation is transmission of heat without any carrier in between, e.g., transmission of heat from sun to the earth's atmosphere.

Radioactivity is the phenomenon of spontaneous disintegration of unstable- atomic nuclei to give more stable product nuclei. It is usually associated with the emission of alpha, beta and gamma rays.

Radio frequency is electromagnetic radiation in the frequency band 3 kilohertz to 300 gigahertz.

Radiography is the production of photographs of the internal structure of bodies, opaque to visible light,. by the radiation from X rays or by gamma rays from radioactive substances.

Raman effect is the phenomenon of scattering of light when monochromatic light passes through a transparent medium.

Reactor is an apparatus for generation of atomic energy.

Rectifier is a device for converting an alternating current into a direct one.

Refraction is a deviation of light passing from one medium into another.

Saturated Vapour is a vapour which is in dynamic equilibrium with its liquid at a given temperature. It can thus hold no more substance in the gaseous phase unless the temperature is raised.

Scalar quantity means quantity which has only magnitude and no direction, e.g., mass, length, etc.

Scattering is the deflection of light energy by fine particles of liquid, solid or gaseous matter from the main direction of a beam.

Short circuit is the direct flow of current between two points of different potential.

Specific heat is the quantity of heat required to raise the temperature of one grain of substance by one degree centigrade.

Static electricity (frictional electricity) is the electricity generated by friction.

Storage battery (accumulator) is a cell which is charged to store electricity by chemical reaction.

Telemetry is a means of making measurement in which the measured quantity is distance from the recording apparatus and the data is sent over a particular telecommunication system from the measuring position to the recording position.

Total internal reflection is the phenomenon in which light when transversing from an optically denser to an optically rarer medium strikes the common surface of the two media at such an angle that it is reflected completely in the former medium.

Transmutation of elements is change of one chemical clement into another.

Ultimate strength is the limited stress at which a material completely fractures or breaks down or crushes.

Ultrasonic Means sound waves of high frequency (12,000 Cycles per second and higher) inaudible to human ear.

Ultraviolet rays are invisible electromagnetic rays of wavelength less than 3,000 angstrom.

Unsaturated vapour is a vapour at a certain temperature that does not contain the maximum amount of the substance in the gaseous phase.

Velocity is the rate of change of position of a body in a given time in a definite direction.

Viscosity is the property of a liquid tending to resist the relative motion within its layers.

Voltage is the electromotive force in electricity.

Valency is the combining ability of an element with respect to hydrogen (e.g., in water, H2O, oxygen has a valency of 2).

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