IGCSE Physics (9-1) Comprehensive Revision Flashcards

Comprehensive vocabulary flashcards covering key definitions, units, laws, and principles across all modules of IGCSE Physics (9-1).

Displacement

The change of position of an object in a particular direction; a vector quantity representing the straight-line distance from start to finish.

Average Speed

The total distance travelled divided by the total time taken to travel that distance: $\text{average speed} = \frac{\text{distance moved}}{\text{time taken}}$.

Instantaneous Speed

The speed of an object measured at a specific moment in time, determined by calculating the ratio of distance travelled over the shortest possible time interval.

Acceleration

The rate at which an object changes its velocity over time: $a = \frac{v - u}{t}$, where $v$ is final velocity, $u$ is initial velocity, and $t$ is time taken.

Deceleration

The rate of decrease of velocity with time, represented numerically as a negative acceleration.

Resultant Force

A single overall force that has the same physical effect as all the individual forces acting on a body combined.

Friction

A force that opposes motion between two surfaces in contact or through fluids, converting kinetic energy into thermal energy.

Terminal Velocity

The constant maximum velocity reached by a falling body when the upward resistive drag force becomes equal and opposite to its downward weight.

Thinking Distance

The distance travelled by a vehicle during the driver's reaction time, from the moment an obstacle is observed until the brakes are applied.

Braking Distance

The distance travelled by a vehicle after the brakes are applied until it comes to a complete standstill.

Momentum

A measure of the motion of an object, calculated as the product of its mass and velocity ($p = m \times v$), measured in $\text{kg}\,\text{m/s}$.

Crumple Zone

A vehicular safety design in the front and rear that collapses during an impact to extend the deceleration time, thereby decreasing the impact force on occupants.

Elastic Collision

A collision between bodies in which the total kinetic energy of the system is conserved before and after impact.

Inelastic Collision

A collision between bodies in which the total kinetic energy is not conserved, with part of the energy transformed into heat, sound, or deformation.

Principle of Conservation of Momentum

The principle stating that in a closed system with no external forces, the total momentum before a collision or explosion equals the total momentum after ($m_1 u_1 + m_2 u_2 = m_1 v_1 + m_2 v_2$).

Newton's Third Law

The law stating that when body A exerts a force on body B, body B exerts an equal and opposite reaction force on body A.

Moment of a Force

The turning effect of a force around a pivot, defined as the product of the force and the perpendicular distance from the pivot to the line of action ($M = F \times d$).

Centre of Gravity

The single point in a body through which the entire weight of the body appears to act.

Hooke's Law

The principle that within the elastic limit of a material, extension is directly proportional to applied force ($e \propto F$).

Elasticity

The property of an object or material that enables it to return to its original shape and size once deforming forces are removed.

Live Wire

The mains electricity conductor that carries high-voltage alternating current into appliances from the power supply.

Neutral Wire

The mains electricity conductor that completes the circuit back to the local substation, remaining close to zero volts.

Earth Wire

A low-resistance safety connection linking the metal chassis of an appliance to the ground, diverting fault currents to trip circuit protection.

Fuse

A safety device containing a thin metal strip with a low melting point that melts and breaks the circuit when current exceeds a predetermined threshold.

Circuit Breaker

An electromagnetic safety switch that opens automatically to interrupt excessive current flow in a circuit and can be reset manually.

Alternating Current (a.c.)

An electric current that repeatedly reverses its direction of flow periodically, such as mains electricity at $50\,\text{Hz}$ and $230\,\text{V}$.

Direct Current (d.c.)

An electric current that continuously flows in a single constant direction, commonly supplied by cells and batteries.

Light-Dependent Resistor (LDR)

A semiconductor sensor whose electrical resistance decreases as incident light intensity increases due to the release of free electrons.

Thermistor

A temperature-sensitive semiconductor resistor whose electrical resistance decreases as its temperature increases.

Volt

The derived SI unit of electric potential difference and electromotive force, defined as one joule of energy transferred per coulomb of charge ($1\,\text{V} = 1\,\text{J/C}$).

Electrostatic Precipitator

An industrial filtration system that charges airborne soot and dust particles negatively so they are attracted to and deposited onto earthed metal collection plates.

Transverse Wave

A wave whose oscillations occur perpendicularly ($90^\circ$) to the direction of wave propagation and energy transfer.

Longitudinal Wave

A wave in which particle vibrations occur parallel to the direction of wave travel, creating alternating regions of compression and rarefaction.

Amplitude

The maximum displacement of a wave particle or field oscillation from its undisturbed equilibrium position.

Wavelength

The physical distance between identical corresponding points on adjacent cycles of a wave, such as from crest to crest, represented by $\lambda$.

Frequency

The number of complete wave cycles or oscillations passing a stationary point per unit of time, measured in hertz ($\text{Hz}$).

Period

The time duration required to complete one full cycle of an oscillation or wave, mathematically expressed as $T = \frac{1}{f}$.

Diffraction

The spreading or curving of wavefronts as they encounter an obstacle or pass through an aperture of dimensions comparable to their wavelength.

Electromagnetic Spectrum

The full continuous distribution of transverse electromagnetic waves travelling at $3 \times 10^8\,\text{m/s}$ in a vacuum, spanning radio waves to gamma rays.

Virtual Image

An optical image formed where light rays appear to diverge from behind an optical element, which cannot be captured on a physical screen.

Refraction

The change of direction of a wave across a medium boundary caused by a difference in wave propagation speed between the two materials.

Refractive Index

A ratio indicating how much a medium slows down light relative to a vacuum, defined by Snell's law as $n = \frac{\sin(i)}{\sin(r)}$.

Critical Angle

The angle of incidence within an optically denser medium at which the refracted ray travels along the boundary surface ($\text{angle of refraction} = 90^\circ$).

Total Internal Reflection

The complete reflection of a light ray back into its optically denser original medium when incident at an angle exceeding the critical angle.

Optical Fibre

A thin flexible glass core enveloped by cladding of lower optical density designed to guide data-carrying light pulses via total internal reflection.

Analogue Signal

An electrical signal that varies continuously in magnitude and frequency to represent information.

Digital Signal

An electrical transmission format consisting of discrete binary pulses switching strictly between two voltages ($0\,\text{V}$ and $5\,\text{V}$), representing $0$ and $1$.

Ultrasound

Sound waves oscillating at frequencies greater than $20{,}000\,\text{Hz}$, exceeding the upper threshold of the human hearing range.

Pitch

The perceptual quality of a sound determined directly by the vibration frequency of the producing sound source.

Thermal Conduction

The transfer of thermal energy through a material without macroscopic movement of the substance itself, mediated by atomic vibrations and free electron transport.

Convection

The mode of heat transfer in fluids (liquids and gases) where heated, less dense fluid expands and rises while cooler, denser fluid descends.

Thermal Radiation

The emission of thermal energy from the surface of bodies via infrared electromagnetic waves that propagate without requiring a material medium.

Sankey Diagram

A visual flow diagram representing the energy inputs, useful energy outputs, and wasted energy of a system, where arrow widths represent proportional energy quantities.

Gravitational Potential Energy (GPE)

The potential energy stored in an object due to its elevated position in a gravitational field: $\text{GPE} = m \times g \times h$.

Kinetic Energy (KE)

The energy possessed by a physical body by virtue of its mass and speed: $\text{KE} = \frac{1}{2} m v^2$.

Power

The rate at which work is done or energy is transferred per unit time: $P = \frac{W}{t}$, measured in watts ($\text{W}$).

Density

The mass of a substance contained within a unit volume: $\rho = \frac{m}{V}$, expressed in units of $\text{kg/m}^3$.

Pressure

The magnitude of normal force applied per unit surface area: $p = \frac{F}{A}$, measured in pascals ($\text{Pa}$).

Brownian Motion

The continuous, erratic, and random motion of microscopic suspended particles resulting from ceaseless collisions with surrounding fluid molecules.

Absolute Zero

The theoretical lowest possible temperature ($0\,\text{K}$ or $-273^\circ\text{C}$) at which particles retain minimal kinetic energy and ideal gas pressure reaches zero.

Magnetic Field

A region surrounding a permanent magnet or electric current within which magnetic forces are exerted on other magnetic materials or moving charges.

Magnetically Hard Material

A substance that requires a strong magnetic field to be magnetised and permanently retains its magnetic polarity once magnetised, such as steel.

Magnetically Soft Material

A substance that is readily magnetised in an external field but quickly loses its induced magnetism when the field is removed, such as iron.

Motor Effect

The physical force exerted on a current-carrying conductor when placed inside a perpendicular magnetic field due to field interference.

Fleming's Left-Hand Rule

A directional rule where the thumb indicates force/motion, the first finger indicates magnetic field (North to South), and the second finger indicates current.

Electromagnetic Induction

The generation of a potential difference across an electrical conductor when it moves through a magnetic field or when the magnetic flux linking it changes.

Transformer

A static electromagnetic device that alters alternating voltages between circuits via electromagnetic induction across primary and secondary coils wound on a soft iron core.

Atomic Number

The number of protons found inside the nucleus of an atom, denoted by $Z$, which defines the chemical identity of an element.

Mass Number

The total count of nucleons (protons and neutrons combined) residing in the atomic nucleus, denoted by $A$.

Isotope

Atoms of the same chemical element sharing identical atomic numbers (protons) but possessing differing mass numbers due to unequal numbers of neutrons.

Alpha Particle

A positively charged nuclear radiation particle consisting of two protons and two neutrons ($^4_2\text{He}$) emitted during the radioactive decay of heavy nuclei.

Beta Particle

A fast-moving electron ($^0_{-1}\text{e}$) ejected from an unstable nucleus when an internal neutron transforms spontaneously into a proton.

Gamma Ray

High-energy, short-wavelength electromagnetic radiation emitted by unstable nuclei to release surplus excitation energy.

Background Radiation

The ubiquitous low-level ionising radiation present continuously in the natural environment from cosmic rays, terrestrial rocks, radon gas, and medical sources.

Geiger-Müller Tube

A radiation detection instrument containing low-pressure inert gas and an anode that converts radiation-induced ionisations into electrical pulses for counting.

Half-Life

The time required for the activity or the number of radioactive nuclei in a radioactive sample to decay to half of its initial value.

Galaxy

A massive gravitationally bound system consisting of billions of stars, planetary systems, gas, and cosmic dust revolving around a common centre.

Supernova

The violent explosion marking the collapse of an aging red supergiant star, expelling gas and dust into space and leaving a neutron star or black hole.

Doppler Effect

The apparent shift in observed frequency and wavelength of a wave caused by relative motion between the emitting source and the receiver.

Redshift

The shift of spectral emission lines toward longer wavelengths (lower frequencies) observed in light from receding astronomical objects, demonstrating the expansion of the universe.

Cosmic Microwave Background (CMB) Radiation

Isotropic microwave radiation detected throughout all of space, representing redshifted thermal radiation left over from the early stages of the Big Bang.