Physics Terminology: Essential Physics Terminology Part-3. More than 200 Terms (from J to O)

Physics Terminology: Essential Physics Terminology Part-3

Physics Terminology

Physics terminology refers to the specialised words and expressions used to describe physical concepts, phenomena, measurements, processes, and laws. These terms provide a precise and standardised language that scientists, students, engineers and researchers use to communicate ideas clearly and accurately.

Because physics deals with the fundamental behaviour of matter, energy, space and time, its vocabulary needs to be exact. Terms such as force, momentum, entropy, frequency, wavelength, resistance, and quantum state each carry specific scientific meanings that differ from their everyday usage. Misunderstanding or misusing these terms can lead to incorrect conclusions or confusion.

Physics terminology is often derived from Latin, Greek, or the names of scientists who made significant contributions-for example, joule, newton, tesla, and curie. Many terms are also linked to mathematical representations, units of measurement or experimental observations.

A good grasp of physics terms helps in:

• Understanding textbooks, lectures and scientific papers
• Solving numerical and conceptual problems
• Describing experiments and results accurately
• Connecting theories with real-world applications
• Communicating clearly in academic, research or technical settings

Overall, physics terminology forms the foundation of effective learning and communication in the subject. Developing familiarity with these terms enables better comprehension of concepts and strengthens one’s ability to apply physics in practical and advanced contexts.

Physics Terminology: More than 200 Terms (from J to O)

Here are more than 200 Terms (from J to O)

Physics Terminology (J)

• Jacket (Thermal)– A protective covering used to reduce heat loss in pipes, reactors, or equipment.
• Jet (Astrophysics)– High-speed streams of particles ejected from stars, black holes, or active galaxies.
• Joule (J)– The SI unit of energy, defined as one newton metre.
• Joule Heating– The process of heat generation when electric current passes through a conductor.
• Junction (Semiconductor)– The boundary between two different types of semiconductor materials, such as p-n junctions.
• Junction Diode– A semiconductor device that allows current to flow in one direction due to a p-n junction.
• Joule’s Law– The law stating that heat produced in a conductor is proportional to the square of the current, resistance, and time.
• Jet Propulsion– Propulsion achieved by expelling matter at high speed in the opposite direction of motion.
• Josephson Effect– The flow of supercurrent between two superconductors separated by a thin insulating barrier.
• Jitter (Signal)– Small fluctuations in wave or signal timing, affecting precision in communication systems.
• Joint Probability (Quantum Physics)– The probability of two events occurring simultaneously in a quantum system.
• Jerk– The rate of change of acceleration with time.
• Joule-Kelvin Effect– The temperature change of a gas when it is allowed to expand without doing external work.
• Jovian Planets– Gas giants like Jupiter and Saturn, studied for gravitational and magnetic physics.
• Jupiter– The largest planet in the Solar System, influencing planetary physics and magnetism studies.
• Jansky– A unit used in radio astronomy to measure spectral flux density.
• Japanese Lantern Model– A visual analogy used to explain specific nuclear or atomic structures.
• Jet Stream– Fast-flowing air currents in the atmosphere affecting fluid dynamics and wave motion.
• Joule-Thomson Expansion– The change in temperature of a real gas when allowed to expand at constant enthalpy.
• Johnson Noise– Random electrical noise generated by the thermal agitation of electrons in a conductor.

Physics Terminology (K)

• Kelvin (K)– The SI unit of thermodynamic temperature, starting from absolute zero.
• Kelvin Effect– The change in vapour pressure caused by the curvature of a liquid surface.
• Kelvin-Planck Statement– A formulation of the second law of thermodynamics regarding heat engines.
• Kepler’s Laws– Three laws describing planetary motion: orbit shapes, areas swept, and orbital periods.
• Kinetic Energy– The energy possessed by an object due to its motion.
• Kinematics– The branch of mechanics describing motion without considering forces.
• Kirchhoff’s Laws– Rules for current and voltage in electrical circuits: Kirchhoff’s Current Law (KCL) and Voltage Law (KVL).
• Kirchhoff’s Current Law (KCL)– States that the sum of currents entering a junction equals the sum leaving it.
• Kirchhoff’s Voltage Law (KVL)– States that the sum of voltages around a closed loop equals zero.
• Klystron– A vacuum tube used to amplify high-frequency radio waves.
• Knudsen Number– A dimensionless number used in fluid dynamics to characterise flow regimes.
• Knot (Speed)– A unit of speed used in maritime and aeronautical physics, equal to one nautical mile per hour.
• Koenig’s Pendulum– A pendulum system used to measure moment of inertia of a rigid body.
• Kondo Effect– An increase in electrical resistance due to magnetic impurities at low temperatures.
• Krypton– A noble gas used in lighting, lasers, and physics experiments.
• Kinematic Viscosity– The ratio of dynamic viscosity to fluid density, indicating fluid resistance to flow.
• Kinematic Wave– A wave describing motion in fluids or traffic flow, based on conservation laws.
• Kinematic Equation– Equations relating displacement, velocity, acceleration, and time.
• Koopman Operator– A mathematical tool used in dynamical systems to study evolution of observables.
• Kelvin-Helmholtz Instability– A fluid instability that occurs at the interface of two fluids moving at different velocities.
• Klein-Gordon Equation– A relativistic wave equation describing spin-0 particles.
• Knudsen Gas– A gas in which the mean free path is comparable to the container size, exhibiting rarefied flow behaviour.
• Kinetic Theory of Gases– A theory explaining gas properties based on particle motion and collisions.
• Kinetic Temperature– Temperature defined through the average kinetic energy of particles.
• Kinematic Chain– A series of linked bodies in motion, analysed in mechanics.
• Kilowatt (kW)– A unit of power equal to 1000 watts.
• Kelvin Probe– An instrument measuring work function or contact potential difference.
• Kerr Effect– The change in refractive index of a material under an applied electric field.
• Kelvin Wave– A wave influenced by Earth’s rotation and gravity, often seen in oceans and atmosphere.
• Klein Bottle– A non-orientable surface with no inside or outside, studied in topology and physics.

Physics Terminology (L)

• Lagrangian– A function representing the difference between kinetic and potential energy in a system, used in mechanics.
• Lagrange Point– A position in space where gravitational forces and orbital motion balance, allowing objects to remain stationary relative to two larger bodies.
• Laser– A device that emits a concentrated, coherent beam of light via stimulated emission.
• Laser Cooling– A technique to reduce the motion of atoms using laser light.
• Laser Doppler Velocimetry– A method to measure the velocity of fluids or particles using laser light.
• Latent Heat– The heat absorbed or released during a phase change without temperature change.
• Law of Conservation of Energy– States that energy cannot be created or destroyed, only transformed.
• Law of Conservation of Momentum– States that the total momentum of a system remains constant in the absence of external forces.
• Law of Gravitation (Newton)– Every mass attracts every other mass with a force proportional to their masses and inversely proportional to the square of the distance between them.
• Law of Reflection– States that the angle of incidence equals the angle of reflection.
• Law of Refraction (Snell’s Law)– Relates the angles of incidence and refraction to the refractive indices of two media.
• Lepton– A fundamental particle, such as electrons or neutrinos, not affected by the strong nuclear force.
• Lenz’s Law– States that induced currents oppose the change causing them.
• Lens– A transparent medium that bends light rays to form an image.
• Levitation– The phenomenon of an object being suspended without support, often using magnetic or aerodynamic forces.
• Liftoff Velocity– The minimum speed required for a rocket to leave a planetary surface.
• Light– Electromagnetic radiation visible to the human eye.
• Light Intensity– The power per unit area carried by a wave, usually in watts per square metre.
• Light Year– The distance that light travels in one year, about 9.46 trillion kilometres.
• Light Wave– An electromagnetic wave that can travel through vacuum or media.
• LIGO (Laser Interferometer Gravitational-Wave Observatory)– An observatory detecting gravitational waves using laser interferometry.
• Linear Momentum– The product of mass and velocity of an object.
• Linear Motion– Motion along a straight line.
• Liquid Crystal– A state of matter with properties between liquids and solids, used in displays.
• Liquid Density– Mass per unit volume of a liquid.
• Lithium– A light metal used in batteries and nuclear physics experiments.
• Load Line (Electronics)– A graphical method to determine the operating point of an electronic device.
• Local Oscillator– A reference signal used in communication receivers for frequency conversion.
• Lorentz Force– The force on a charged particle due to electric and magnetic fields.
• Lorentz Transformation– Mathematical equations relating space and time coordinates between moving reference frames.
• Loudness– The human perception of sound intensity.
• Luminescence– Emission of light by a substance not caused by heat.
• Luminance– The amount of light emitted or reflected from a surface per unit area in a given direction.
• Luminous Flux– The measure of perceived power of light, measured in lumens.
• Lyman Series– A series of ultraviolet spectral lines of hydrogen due to electron transitions to the ground state.
• Lyot Filter– An optical filter used for isolating specific wavelengths of light.
• Lagrange Multiplier (Physics)– A technique in mechanics to handle constraints in optimisation problems.
• Laminar Flow– Smooth, orderly motion of fluid layers without turbulence.
• Laser Interferometry– A method to measure small displacements, changes in refractive index, or gravitational waves using laser interference.
• Laser Trapping– Using laser beams to manipulate microscopic particles or atoms.

Physics Terminology (M)

• Magnet– An object that produces a magnetic field, attracting ferromagnetic materials.
• Magnetic Field– A region around a magnet or current-carrying conductor where magnetic forces can be detected.
• Magnetic Flux– The total magnetic field passing through a given area.
• Magnetic Flux Density– The amount of magnetic flux per unit area, measured in tesla (T).
• Magnetic Moment– A measure of the strength and orientation of a magnetic source.
• Magnetic Resonance Imaging (MRI)– A medical imaging technique using strong magnetic fields and radio waves.
• Magnetohydrodynamics– The study of the behaviour of electrically conducting fluids in magnetic fields.
• Magnetron– A device generating microwaves, commonly used in microwave ovens and radar.
• Major Axis– The longest diameter of an ellipse or orbital path.
• Malus’s Law– Describes the intensity of light transmitted through a polariser as a function of angle.
• Manometer– An instrument for measuring pressure differences in fluids.
• Mass– The quantity of matter in an object, often measured in kilograms.
• Mass Defect– The difference between the mass of a nucleus and the sum of its constituent nucleons.
• Mass Number– The total number of protons and neutrons in an atomic nucleus.
• Mass Spectrometer– An instrument used to measure masses of particles and isotopic composition.
• Mathematical Pendulum– A simple pendulum used to study oscillatory motion and gravitational acceleration.
• Maximum Height– The highest point reached by a projectile in its trajectory.
• Mechanical Advantage– The ratio of output force to input force in a mechanical system.
• Mechanical Energy– The sum of kinetic and potential energy in a system.
• Mechanical Oscillator– A device or system that exhibits repetitive motion under a restoring force.
• Mechanical Work– The product of force and displacement in the direction of force.
• Medium (Wave)– The substance or material through which a wave propagates.
• Melting Point– The temperature at which a solid turns into a liquid.
• Meniscus– The curved surface of a liquid in a container, important for accurate measurement.
• Mercury Barometer– A device that measures atmospheric pressure using a column of mercury.
• Meson– A subatomic particle composed of a quark and an antiquark, mediating strong forces.
• Metallurgy Physics– Study of physical properties of metals and their behaviour under various forces.
• Microgravity– Extremely low gravity conditions, such as those in orbiting spacecraft.
• Microwave– Electromagnetic waves with wavelengths between infrared and radio waves.
• Microwave Oven– A device using microwaves to heat food via dielectric heating.
• Millikan Oil Drop Experiment– An experiment that measured the electric charge of an electron.
• Millimetre Wave– Electromagnetic waves with wavelengths in the millimetre range, used in radar and communication.
• Mirror– A reflective surface that forms images by reflecting light.
• Moment of Inertia– A measure of an object’s resistance to rotational motion.
• Momentum– The product of mass and velocity of an object, a conserved quantity in isolated systems.
• Monochromatic Light– Light consisting of a single wavelength or colour.
• Monopole (Magnetic)– A hypothetical particle with only one magnetic pole.
• Moon (Earth’s)– A natural satellite affecting tides and orbital physics.
• Motion– The change in position of an object with respect to a reference frame.
• Muon– A heavy lepton similar to the electron but with greater mass.
• Mutual Inductance– The ability of one coil to induce an electromotive force in another nearby coil.
• Molecular Mass– The mass of a molecule, calculated as the sum of its atomic masses.
• Molecular Orbital– A region in a molecule where electrons are likely to be found.
• Molecular Vibration– The periodic motion of atoms within a molecule.
• Muon Collider– A theoretical particle accelerator using muons for high-energy collisions.
• Muon Neutrino– A type of neutrino associated with muons.
• Magnetopause– The boundary between Earth’s magnetosphere and the solar wind.
• Magnetosphere– The region around a planet dominated by its magnetic field.
• Magnetostriction– The change in shape or dimensions of a ferromagnetic material when magnetised.
• Maxwell’s Equations– A set of four equations describing the behaviour of electric and magnetic fields.

Physics Terminology (N)

• Nanotechnology– The study and application of materials and devices at the nanometre scale.
• Nanosecond (ns)– One billionth of a second, commonly used in high-speed measurements.
• Natural Frequency– The frequency at which a system tends to oscillate in the absence of external forces.
• Negative Charge– An electric charge carried by electrons, opposite to positive charge.
• Neon– A noble gas often used in lighting and plasma physics.
• Neutrino– A nearly massless, neutral subatomic particle that interacts very weakly with matter.
• Neutron– A neutral subatomic particle found in atomic nuclei.
• Neutron Activation– The process by which stable nuclei capture neutrons and become radioactive.
• Neutron Star– A dense stellar remnant composed primarily of neutrons, formed after a supernova.
• Newton (N)– The SI unit of force, defined as 1 kg\cdotpm/s²1kg\cdotpm/s².
• Newton’s First Law– States that an object remains at rest or in uniform motion unless acted upon by a force.
• Newton’s Second Law– States that force equals mass times acceleration (F=maF=ma).
• Newton’s Third Law– States that every action has an equal and opposite reaction.
• Newtonian Mechanics– Classical physics describing motion based on Newton’s laws.
• Newtonian Fluid– A fluid whose viscosity remains constant regardless of applied stress.
• Newtonian Telescope– A reflecting telescope design invented by Isaac Newton.
• Nodal Point– A point on a standing wave or in an optical system where amplitude is zero.
• Noise (Physics)– Unwanted random disturbances that interfere with signals or measurements.
• Non-Newtonian Fluid– A fluid whose viscosity changes with applied stress or strain rate.
• Normal Force– The perpendicular force exerted by a surface on an object in contact.
• Nuclear Binding Energy– The energy required to separate a nucleus into its constituent protons and neutrons.
• Nuclear Fission– The splitting of a heavy nucleus into smaller nuclei with energy release.
• Nuclear Fusion– The combination of light nuclei to form a heavier nucleus, releasing energy.
• Nuclear Magnetic Resonance (NMR)– A technique using magnetic fields and radio waves to study atomic nuclei.
• Nuclear Reactor– A device that initiates and controls a sustained nuclear chain reaction.
• Nuclear Shell Model– A model describing the structure of atomic nuclei in terms of energy levels.
• Nucleon– A proton or neutron in an atomic nucleus.
• Nucleon Spin– The intrinsic angular momentum of a proton or neutron.
• Nucleosynthesis– The process of forming new atomic nuclei from pre-existing nucleons.
• Nuclear Physics– The branch of physics studying atomic nuclei and their interactions.
• Number Density– The number of particles per unit volume in a substance or system.
• Newton Rings– Interference patterns formed between a convex lens and a flat surface.
• Nodal Line– A line in a wave pattern where displacement is consistently zero.
• Newtonian Gravity– The classical model of gravitational attraction between masses.
• Newtonian Limit– The approximation where relativistic effects are negligible, and classical physics applies.
• Neutron Diffraction– A technique using neutrons to study atomic and magnetic structures.
• Neutral Particle– A particle with no net electric charge, such as neutrons or photons.
• Negative Feedback– A process that counteracts changes in a system to maintain stability.
• Noise Figure– A measure of degradation of the signal-to-noise ratio in an electronic system.
• Nonlinear Optics– The study of light interaction with materials where the response is nonlinear.
• Nuclear Density– The mass per unit volume of atomic nuclei.
• Nuclear Equation– A symbolic representation of a nuclear reaction showing reactants and products.
• Nuclear Force– The strong force that binds protons and neutrons together in a nucleus.
• Nuclear Spin– The intrinsic angular momentum of an atomic nucleus.
• Neutralino– A hypothetical particle in supersymmetric theories, potentially a dark matter candidate.
• Neutron Star Merger– The collision of two neutron stars, producing gravitational waves and heavy elements.
• Nuclear Binding Energy per Nucleon– The average energy holding each nucleon in a nucleus.
• Neutron Flux– The number of neutrons passing through a unit area per unit time.
• Neutral Atom– An atom with equal numbers of protons and electrons.
• Newton’s Law of Cooling– Describes the rate at which a body loses heat proportional to temperature difference with the environment.

Physics Terminology (O)

• Objective Lens– The primary lens in a microscope or telescope that forms the initial image of an object.
• Oblique Incidence– When a wave strikes a surface at an angle other than 90 degrees.
• Observational Astronomy– The study of celestial objects through direct observation using telescopes or detectors.
• Ocean Currents– Large-scale flow of seawater influenced by wind, Earth’s rotation, and temperature differences.
• Ohm (Ω)– The SI unit of electrical resistance, defined as one volt per ampere.
• Ohm’s Law– The principle stating that current through a conductor is directly proportional to voltage and inversely proportional to resistance.
• Ohmmeter– An instrument used to measure electrical resistance.
• Omega (Ω) Particle– A subatomic particle consisting of three strange quarks.
• Optical Axis– A line passing through the centres of curvature of lens or mirror surfaces.
• Optical Fibre– A thin strand of glass or plastic that transmits light signals over long distances.
• Optical Illusion– A visual perception that differs from reality due to light behaviour.
• Optical Instrument– A device that uses light to magnify, observe, or analyse objects.
• Optical Path– The product of the physical distance a light ray travels and the refractive index of the medium.
• Optical Power– The ability of a lens to converge or diverge light, measured in dioptres.
• Optical Tweezers– A tool that uses laser beams to manipulate microscopic particles.
• Orbit– The curved path of an object around a celestial body due to gravitational forces.
• Oscillation– Repetitive variation of a quantity around a central value, such as motion of a pendulum.
• Oscilloscope– An instrument that displays voltage signals as a function of time.
• Output Energy– The usable energy produced by a system after energy transformations.
• Overtone– A frequency higher than the fundamental frequency in a vibrating system.
• Overpressure– Pressure in excess of the normal atmospheric pressure, often in explosions or waves.
• Overtones in Acoustics– Harmonics produced along with the fundamental frequency of a vibrating system.
• Oxidation– The loss of electrons by a chemical species, often producing energy in electrochemical systems.
• Oscillatory Motion– Motion that repeats in a regular pattern around an equilibrium point.
• Ohmic Material– A material that obeys Ohm’s Law, showing linear current-voltage characteristics.
• Optical Density– A measure of a material’s ability to absorb light.
• Optical Axis of a Lens– A straight line passing through the centre of curvature of lens surfaces.
• Optical Interference– The superposition of light waves producing patterns of reinforcement or cancellation.
• Optical Activity– The ability of a substance to rotate the plane of polarized light.
• Optical Resolution– The ability of an optical system to distinguish between two closely spaced points.
• Optical Spectrum– The range of wavelengths of electromagnetic radiation visible as light.
• Optomechanics– The study and application of mechanical systems interacting with light.
• Opacity– The measure of transparency or how much light is blocked by a material.
• Orbital Angular Momentum– The angular momentum of an electron in its orbit around a nucleus.
• Orbital Period– The time taken for an object to complete one full orbit around another body.
• Orbital Velocity– The velocity needed for an object to stay in orbit around a celestial body.
• Oscillograph– An instrument that records electrical oscillations over time.
• Overdamped System– A system in which oscillations decay without completing a single cycle due to high damping.
• Overvoltage– A voltage exceeding the normal operating limit of an electrical device.
• Oxide Layer– A thin layer of oxygen compound on a material surface affecting electrical or thermal properties.
• Ohmic Heating– Heating due to the passage of electric current through a conductor.
• Optical Bench– A laboratory setup for conducting optical experiments with lenses and mirrors.
• Optical Trapping– Using focused light beams to hold or manipulate microscopic particles.
• Oscillatory Circuit– An electrical circuit designed to produce periodic voltage or current variations.
• Oscillatory System– Any system exhibiting repetitive motion around an equilibrium.
• Orbital Mechanics– The study of motion of objects under the influence of gravitational forces.
• Optical Path Difference– The difference in path lengths taken by two light waves causing interference.
• Optical Phenomena– Events like reflection, refraction, diffraction, and polarization observed with light.
• Optical Pumping– The process of using light to excite electrons to higher energy levels.
• Overpotential– The extra voltage required to drive a non-spontaneous electrochemical reaction.

Conclusion 

Physics terminology is not just vocabulary – it is the backbone of understanding and communicating scientific ideas with clarity and precision. Each term represents a well-defined concept, law, measurement, or phenomenon, helping to eliminate ambiguity and foster accurate interpretation across education, research, and application.

From classical mechanics and thermodynamics to quantum theory and astrophysics, mastery of terminology allows learners and professionals to:

• Grasp complex ideas more easily
• Connect theory with real-world observations
• Interpret scientific data correctly
• Communicate findings with consistency and confidence
• Build a strong foundation for advanced study or research

In essence, physics terminology serves as the universal language of the physical sciences. Whether used in classrooms, laboratories, engineering fields, or space research, these terms empower individuals to explore, explain and expand our understanding of the universe.

Go to Essential Physics Terminology Part-1 ( A to E)

Go to Essential Physics Terminology Part-2 (F to I)

Go to Essential Physics Terminology Part-4 (P to S)

Go to Essential Physics Terminology Part-5 (T to Z)

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