PHYSICS 9702 Glossary
Key physics terms used throughout the syllabus. Definitions follow the Cambridge-style glossary format to help you quickly revise important concepts.
Absolute uncertainty
The margin of uncertainty expressed in the same units as the measured quantity.
Acceleration
The rate of change of velocity with respect to time.
Acceleration of free fall
The acceleration experienced by an object solely under the influence of gravity.
Accuracy
The closeness of a measured value to the true value of the quantity.
Air resistance
A type of drag force acting on objects as they move through air.
Alpha radiation
Radiation consisting of helium nuclei (two protons and two neutrons) emitted from unstable nuclei.
Amplitude
The maximum displacement of a point on a wave from its equilibrium position.
Antineutrino
The antiparticle of the neutrino, produced in certain types of radioactive decay.
Antinode
A point on a stationary wave where the displacement reaches a maximum amplitude.
Antiparticle
A particle with the same mass as a corresponding particle but with opposite charge and quantum numbers.
Antiquark
The antiparticle of a quark, with opposite charge and quantum numbers.
Archimedes’ principle
The principle stating that the upthrust on an object immersed in a fluid is equal to the weight of fluid displaced by the object.
Area under a graph
The region between a graph and the axis, representing a physical quantity such as displacement when considering a velocity–time graph.
Baryon
A hadron consisting of three quarks.
Base quantity
A fundamental physical quantity in the SI system from which all other quantities are derived.
Beta-minus radiation
Radiation consisting of electrons emitted from the nucleus during the decay of a neutron into a proton.
Beta-plus radiation
Radiation consisting of positrons emitted from the nucleus during the decay of a proton into a neutron.
Centre of gravity
The point at which the entire weight of an object may be considered to act.
Charge carrier
A particle that carries electric charge, such as an electron or ion, and is responsible for electric current in a material.
Coherence
A property of two or more waves in which the phase difference between them remains constant over time.
Component of a vector
The projection of a vector along a specified axis, representing its effect in that direction.
Compression
The decrease in length of a material when subjected to a compressive force.
Compressive force
A force that acts to compress or shorten a material.
Conservation of charge
The principle that the total electric charge remains constant in nuclear processes.
Conservation of energy
The principle that energy cannot be created or destroyed, only transformed from one form to another.
Conservation of momentum
The total momentum of a system remains constant provided no external force acts on it.
Conservation of nucleon number
The principle that the total number of nucleons remains constant in nuclear processes.
Coplanar vectors
Vectors that lie in the same plane.
Couple
A pair of equal and opposite forces whose lines of action do not coincide, producing rotation only.
Deformation
A change in the shape or length of a material due to an applied force.
Density
Mass per unit volume of a substance.
Derived unit
A unit obtained by combining SI base units according to the physical relationship between quantities.
Diffraction
The spreading of waves as they pass through a gap or around an obstacle.
Diffraction grating
An optical device consisting of a large number of equally spaced parallel slits that diffract light to produce interference patterns.
Displacement
The change in position of an object in a specified direction; a vector quantity.
Distance
The total length of the path travelled by an object, irrespective of direction.
Doppler effect
The change in observed frequency of a wave when there is relative motion between the source and the observer.
Drag force
A resistive force acting opposite to the motion of an object moving through a fluid.
Efficiency
The ratio of useful energy output to total energy input.
Elastic collision
A collision in which both momentum and total kinetic energy are conserved.
Elastic deformation
Deformation that is reversible when the applied force is removed.
Elastic limit
The maximum stress or force that a material can withstand and still return to its original shape when the force is removed.
Elastic potential energy
The energy stored in a material as a result of reversible deformation.
Electric current
The rate of flow of electric charge through a conductor.
Electromagnetic spectrum
The continuous range of wavelengths or frequencies of electromagnetic waves, from radio waves to gamma rays.
Electromagnetic wave
A transverse wave consisting of oscillating electric and magnetic fields that travels at the speed of light in free space.
Electromotive force
The energy transferred by a source to each unit charge as it moves around a complete circuit.
Electromotive force (e.m.f.)
The energy supplied per unit charge by a source in driving charge around a complete circuit.
Electron
A negatively charged fundamental particle that orbits the nucleus of an atom.
Energy
The capacity to do work.
Equilibrium
The state in which the resultant force and the resultant torque acting on a system are both zero.
Extension
The increase in length of a material when subjected to a tensile force.
Filament lamp
An electrical component in which resistance increases with increasing current due to temperature rise of the filament.
Force
An interaction that causes a change in the motion of an object.
Force–extension graph
A graph showing the relationship between the force applied to a material and the resulting extension.
Free fall
Motion of a body under the influence of gravitational force only.
Frequency
The number of complete cycles of a wave passing a point per unit time.
Frictional force
A force that opposes the relative motion between two surfaces in contact.
Fringe
A bright or dark band produced on a screen as a result of constructive or destructive interference of waves.
Galvanometer
A sensitive instrument used to detect and measure small electric currents.
Gamma radiation
Electromagnetic radiation of very high frequency emitted from the nucleus during radioactive decay.
Gradient
The slope of a graph, representing the rate of change of the quantity on the y-axis with respect to the x-axis.
Gravitational field
A region of space where a mass experiences a force due to gravity.
Gravitational potential energy
The energy possessed by a mass due to its position in a gravitational field.
Hadron
A particle composed of quarks, held together by the strong force; includes baryons and mesons.
Homogeneity
The property of an equation in which all terms have the same dimensions or units.
Hooke’s law
The principle that the extension of a material is proportional to the applied force, provided the limit of proportionality is not exceeded.
Hydrostatic pressure
The pressure exerted by a fluid at rest due to the weight of the fluid above a given point.
Inelastic collision
A collision in which momentum is conserved but total kinetic energy is not.
Intensity
The power transmitted per unit area perpendicular to the direction of energy transfer by a wave.
Interference
The phenomenon in which two or more waves superpose to form a resultant wave of greater, lower, or the same amplitude.
Internal resistance
The resistance to current within a source of electromotive force, causing a loss of potential difference inside the source.
Isotope
Atoms of the same element with the same number of protons but different numbers of neutrons.
Kinetic energy
The energy possessed by an object due to its motion.
Kirchhoff’s first law
The sum of currents entering a junction is equal to the sum of currents leaving the junction.
Kirchhoff’s second law
The sum of the electromotive forces in any closed loop is equal to the sum of the potential differences in that loop.
Lepton
A fundamental particle that does not experience the strong interaction, such as the electron or neutrino.
Light-dependent resistor
A resistor whose resistance decreases as the intensity of incident light increases.
Light-dependent resistor (LDR)
A resistor whose resistance decreases as the intensity of incident light increases.
Limit of proportionality
The maximum force for which extension is directly proportional to load.
Linear momentum
The product of an object's mass and its velocity.
Load
The force applied to a material that causes deformation.
Longitudinal wave
A wave in which the oscillations are parallel to the direction of energy transfer.
Mass
A measure of the amount of matter in an object and its resistance to a change in motion.
Meson
A hadron consisting of one quark and one antiquark.
Moment of a force
The product of the force and the perpendicular distance from the pivot to the line of action of the force.
Neutrino
A neutral, nearly massless fundamental particle produced in certain types of radioactive decay.
Neutron
An uncharged subatomic particle found in the nucleus of an atom.
Newton’s first law of motion
An object remains at rest or in uniform motion in a straight line unless acted on by a resultant force.
Newton’s second law of motion
The rate of change of momentum of an object is proportional to the resultant force acting on it and occurs in the direction of the force.
Newton’s third law of motion
When two bodies interact, they exert equal and opposite forces on each other.
Node
A point on a stationary wave where the displacement is always zero.
Nucleon
A collective term for protons and neutrons in the nucleus.
Nucleon number
The total number of protons and neutrons in the nucleus of an atom.
Nucleus
The small, dense central region of an atom containing protons and neutrons.
Nuclide notation
A representation of a nucleus using the format A/Z X, where A is the nucleon number, Z is the proton number, and X is the chemical symbol.
Number density
The number of charge carriers per unit volume in a material.
Ohm’s law
The statement that the current through a conductor is proportional to the potential difference across it, provided physical conditions remain constant.
Parallel circuit
A circuit in which components are connected across common points, providing separate paths for current.
Path difference
The difference in distance traveled by two waves from their sources to a given point.
Percentage uncertainty
The absolute uncertainty expressed as a percentage of the measured value.
Period
The time taken for one complete cycle of a wave to pass a given point.
Phase difference
The fraction of a cycle by which one wave leads or lags another, usually measured in degrees or radians.
Physical quantity
A property of a material or system that can be measured and expressed as a numerical value with a unit.
Plane-polarised wave
A transverse wave in which the oscillations occur in a single plane perpendicular to the direction of propagation.
Plastic deformation
Deformation that is permanent after the applied force is removed.
Polarisation
The phenomenon in which the oscillations of a transverse wave are restricted to a single plane.
Positron
The antiparticle of the electron, with the same mass and a positive charge.
Potential difference
The energy transferred per unit charge as charge moves between two points in a circuit.
Potential divider
A circuit arrangement that divides the input potential difference into parts proportional to the resistances used.
Potentiometer
A device or circuit used to compare potential differences by balancing them against a known potential difference.
Power
The rate at which work is done or energy is transferred.
Precision
The degree of consistency or repeatability of measurements of the same quantity.
Prefix
A symbol placed before a unit to indicate a decimal multiple or submultiple of that unit.
Pressure
Force per unit area acting normally to a surface.
Principle of moments
For a body in equilibrium, the sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about that point.
Progressive wave
A wave that transfers energy through a medium or space as it moves away from the source.
Proton
A positively charged subatomic particle found in the nucleus of an atom.
Proton number
The number of protons in the nucleus of an atom, also known as atomic number.
Quantisation of charge
The property that electric charge exists only in discrete amounts, which are integer multiples of the elementary charge.
Quark
A fundamental particle that is a constituent of hadrons, existing in six flavours: up, down, strange, charm, top, and bottom.
Random error
An error that causes measurements to vary unpredictably about the true value.
Resistance
The ratio of the potential difference across a component to the current through it.
Resistivity
A property of a material that quantifies how strongly it resists electric current, defined as the resistance of a unit length and unit cross-sectional area.
Resultant force
The single force that has the same effect as all the forces acting on an object combined.
Resultant vector
A single vector that has the same effect as two or more vectors combined.
Scalar
A physical quantity that has magnitude only and no direction.
Semiconductor diode
A component that allows current to flow more easily in one direction than the other, exhibiting non-ohmic behaviour.
Series circuit
A circuit in which components are connected end-to-end so that the same current flows through each component.
SI unit
A unit defined by the International System of Units, used as a standard for measuring physical quantities.
Speed
The rate of change of distance with respect to time; a scalar quantity.
Spring constant
A measure of the stiffness of a spring, defined as the ratio of force to extension.
Stationary wave
A wave pattern produced by the superposition of two waves of the same frequency and amplitude traveling in opposite directions, resulting in points of no displacement (nodes) and points of maximum displacement (antinodes).
Strain
The extension per unit original length of a material.
Stress
The force applied per unit cross-sectional area of a material.
Superposition
The principle that when two or more waves overlap, the resultant displacement at any point is the vector sum of the displacements due to each wave.
Systematic error
An error that causes measurements to differ from the true value by a consistent amount in the same direction.
Tensile force
A force that acts to stretch a material.
Terminal potential difference
The potential difference measured across the terminals of a source of electromotive force when a current is flowing.
Terminal velocity
The constant velocity reached when the resistive forces on a moving object balance the driving force.
Thermistor
A resistor whose resistance decreases as its temperature increases, typically having a negative temperature coefficient.
Torque of a couple
The product of one of the forces and the perpendicular distance between their lines of action.
Transverse wave
A wave in which the oscillations are perpendicular to the direction of energy transfer.
Uncertainty
An estimate of the range within which the true value of a measured quantity lies.
Unified atomic mass unit
A unit of mass equal to one twelfth of the mass of a carbon-12 atom.
Uniform acceleration
Acceleration that remains constant in magnitude and direction.
Uniform gravitational field
A region in which the gravitational field strength is constant in magnitude and direction.
Upthrust
The upward force exerted by a fluid on an object submerged in it, equal to the weight of fluid displaced.
Vector
A physical quantity that has both magnitude and direction.
Vector triangle
A geometric representation in which three coplanar forces in equilibrium are arranged tip-to-tail to form a closed triangle.
Velocity
The rate of change of displacement with respect to time; a vector quantity.
Wave
A disturbance that transfers energy from one place to another without the transfer of matter.
Wave speed
The speed at which a wave propagates through a medium.
Wavelength
The distance between two consecutive points in phase on a wave, such as crest to crest or compression to compression.
Weight
The force on a mass due to a gravitational field.
Work
The product of the force and the displacement in the direction of the force.
Young modulus
The ratio of stress to strain for a material within the limit of proportionality.
Zero error
A systematic error that occurs when a measuring instrument does not read zero when the quantity measured is zero.
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