IGCSE physics

Speed

The distance travelled per unit time. A scalar quantity calculated by $v = \frac{s}{t}$, measured in $\text{m/s}$.

Velocity

The speed of an object in a specified direction. A vector quantity calculated by displacement divided by time, measured in $\text{m/s}$.

Acceleration

The rate of change of velocity with respect to time. A vector quantity calculated by $a = \frac{v - u}{t}$, measured in $\text{m/s}^2$.

Newton's First Law of Motion

An object remains at rest or continues to move with uniform velocity unless acted upon by an unbalanced resultant force.

Newton's Second Law of Motion

The resultant force acting on an object equals the product of its mass and acceleration: $F = ma$, measured in newtons ($\text{N}$).

Newton's Third Law of Motion

When body A exerts a force on body B, body B exerts an equal in magnitude and opposite in direction force on body A.

Weight

The downward gravitational force acting on an object's mass in a gravitational field: $W = mg$.

Density

The mass per unit volume of a material: $\rho = \frac{m}{V}$, measured in $\text{kg/m}^3$ or $\text{g/cm}^3$.

Momentum

The product of an object's mass and its velocity: $p = mv$, measured in $\text{kg}\cdot\text{m/s}$ or $\text{N}\cdot\text{s}$.

Principle of Conservation of Momentum

The total momentum of an isolated system before a collision equals the total momentum after the collision, provided no external resultant forces act.

Impulse

The product of the resultant force and the time interval for which it acts, which equals the change in momentum: $\text{Impulse} = F\Delta t = \Delta p$.

Hooke's Law

The extension of a spring is directly proportional to the applied tensile force up to the limit of proportionality: $F = kx$.

Limit of Proportionality

The point beyond which extension is no longer directly proportional to the applied force under Hooke's Law.

Elastic vs Plastic Deformation

In elastic deformation, an object returns to its original dimensions when the deforming force is removed; in plastic deformation, permanent change in shape remains.

Moment of a Force

The turning effect of a force about a pivot, equal to the force multiplied by the perpendicular distance to the pivot: $\text{Moment} = Fd$, measured in $\text{N}\cdot\text{m}$.

Principle of Moments

For a system in rotational equilibrium, the sum of clockwise moments about any point equals the sum of anticlockwise moments about that same point.

Center of Gravity

The single point through which the entire weight of an object can be considered to act.

Conditions for Equilibrium

An object is in complete equilibrium when the resultant force acting on it is zero ($\Sigma F = 0$) and the resultant moment about any pivot is zero ($\Sigma M = 0$).

Centripetal Force

The resultant inward force directed toward the center of a circular path that maintains an object's uniform circular motion.

Terminal Velocity

The constant maximum velocity reached by a falling body when the upward resistive forces equal the downward gravitational force, giving zero acceleration.

Work Done

The energy transferred when a force moves an object through a distance in the direction of the force: $W = Fd$, measured in joules ($\text{J}$).

Kinetic Energy

The energy possessed by an object due to its motion: $E_k = \frac{1}{2}mv^2$, measured in joules ($\text{J}$).

Gravitational Potential Energy

The energy stored in an object due to its position within a gravitational field: $E_p = mgh$, measured in joules ($\text{J}$).

Principle of Conservation of Energy

Energy cannot be created or destroyed, only transferred from one store to another; the total energy of a closed system remains constant.

Power

The rate of doing work or transferring energy per unit time: $P = \frac{W}{t} = \frac{E}{t}$, measured in watts ($\text{W}$) where $1\,\text{W} = 1\,\text{J/s}$.

Efficiency

The ratio of useful output to total input for a device: $\text{Efficiency} = \left(\frac{\text{Useful Energy Output}}{\text{Total Energy Input}}\right) \times 100\%$.

Pressure

The normal force applied per unit area: $p = \frac{F}{A}$, measured in pascals ($\text{Pa}$) where $1\,\text{Pa} = 1\,\text{N/m}^2$.

Liquid Pressure Formula

The pressure exerted at depth $h$ in a fluid of density $\rho$: $p = \rho gh$.

Brownian Motion

The continuous, erratic, random motion of microscopic particles suspended in a fluid, caused by collisions with fast, unseen fluid molecules.

Absolute Zero

The lowest possible theoretical temperature ($0\,\text{K}$ or $-273\,^\circ\text{C}$) at which particles possess minimum internal kinetic energy.

Kelvin Temperature Scale Conversion

The absolute temperature conversion given by $T = \theta + 273$, where $T$ is in kelvin ($\text{K}$) and $\theta$ is in Celsius ($^\circ\text{C}$).

Thermal Conduction

The transfer of thermal energy through matter via microscopic collisions of particles and free delocalized electron diffusion (mainly in metals).

Convection

The transfer of thermal energy in fluids driven by density differences, where warmer, less dense fluid rises and cooler, denser fluid sinks.

Thermal Radiation

The emission of infrared electromagnetic waves by all matter above absolute zero, requiring no material medium to travel.

Specific Heat Capacity

The thermal energy needed to change the temperature of $1\,\text{kg}$ of a substance by $1\,^\circ\text{C}$: $\Delta E = mc\Delta T$, measured in $\text{J/(kg}\cdot^\circ\text{C)}$.

Thermal Capacity

The thermal energy needed to raise the temperature of an entire object by $1\,^\circ\text{C}$: $C = mc$.

Specific Latent Heat

The energy required to change the physical state of $1\,\text{kg}$ of a substance at constant temperature: $\Delta E = mL$, measured in $\text{J/kg}$.

Boiling vs Evaporation

Boiling takes place throughout the entire bulk of a liquid at a specific boiling point; evaporation occurs only at the liquid surface at any temperature.

Boyle's Law

For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume: $p_1 V_1 = p_2 V_2$.

Transverse Wave

A wave in which oscillations are perpendicular to the direction of wave travel and energy transfer (e.g., surface water ripples, electromagnetic waves).

Longitudinal Wave

A wave in which oscillations are parallel to the direction of wave travel, creating alternating compressions and rarefactions (e.g., sound waves).

Wave Equation

Relates wave velocity, frequency, and wavelength: $v = f\lambda$.

Law of Reflection

The angle of incidence is equal to the angle of reflection ($i = r$), measured relative to the normal line.

Snell's Law / Refractive Index

The ratio of the sine of the angle of incidence to the sine of the angle of refraction: $n = \frac{\sin(i)}{\sin(r)}$.

Critical Angle and Total Internal Reflection

Occurs when light attempts to travel from an optically denser to a less dense medium at an incident angle greater than the critical angle ($c$), where $\sin(c) = \frac{1}{n}$.

Diffraction

The spreading of wave fronts as they pass by an obstacle or through an aperture, being greatest when gap size is comparable to the wavelength.

Real Image vs Virtual Image

A real image is formed by converging light rays and can be cast onto a screen; a virtual image is formed by rays that only appear to diverge from a point and cannot be projected.

Dispersion of Light

The splitting of polychromatic light into its component wavelengths by a prism because different wavelengths travel at different speeds and refract by different amounts.

Human Auditory Range

The frequency range of sound audible to a typical human ear, spanning from $20\,\text{Hz}$ to $20\,000\,\text{Hz}$.

Electric Current

The rate of flow of electric charge past a point in an electric circuit: $I = \frac{Q}{t}$, measured in amperes ($\text{A}$).

Potential Difference (Voltage)

The work done or energy transferred per unit charge passing between two points: $V = \frac{W}{Q}$, measured in volts ($\text{V}$).

Ohm's Law

The electric current through an ohmic conductor is directly proportional to the potential difference across it at constant temperature: $V = IR$.

Resistance in Series

The total resistance of components connected end-to-end: $R_{\text{total}} = R_1 + R_2 + R_3 + \dots$

Resistance in Parallel

The effective resistance across parallel branches: $\frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2} + \dots$

Electrical Power

The rate of electrical energy dissipation in a circuit: $P = IV = I^2R = \frac{V^2}{R}$, measured in watts ($\text{W}$).

Fleming's Left-Hand Rule

Used for motors: Thumb points in the direction of Motion/Force, First finger indicates Magnetic Field ($\text{N}$ to $\text{S}$), and Second finger indicates Conventional Current.

Split-Ring Commutator

A component in a DC motor that reverses the direction of current in the rotating coil every half-turn to produce continuous unidirectional rotation.

Fleming's Right-Hand Rule

Used for generators: Thumb indicates Motion of conductor, First finger indicates Magnetic Field ($\text{N}$ to $\text{S}$), and Second finger indicates Induced Current.

Lenz's Law

The direction of an induced electromotive force or current is always such that its magnetic effect opposes the change that created it.

Transformer Voltage Ratio

The relationship governing primary and secondary turns and voltages in a transformer: $\frac{V_p}{V_s} = \frac{N_p}{N_s}$.

High Voltage Power Transmission Rationale

Transmitting electrical power at high voltage reduces current ($P = IV$), which minimizes resistive heating losses in transmission cables ($P_{\text{loss}} = I^2R$).

Alpha Particle ($\alpha$)

A helium nucleus consisting of $2$ protons and $2$ neutrons with a charge of $+2$; highly ionizing and stopped by a single sheet of paper.

Beta Particle ($\beta^-$)

A fast-moving electron emitted from an unstable nucleus when a neutron transforms into a proton; moderately ionizing and stopped by a few millimeters of aluminum.

Gamma Ray ($\gamma$)

High-frequency electromagnetic radiation emitted from an excited nucleus; weakly ionizing and highly penetrating, attenuated by thick lead or meters of concrete.

Radioactive Half-Life

The average time required for half the unstable nuclei in a sample to decay, or for the activity of the sample to drop to half its initial value.

Nuclear Fission vs Nuclear Fusion

Nuclear fission is the splitting of a heavy unstable nucleus into smaller daughter nuclei; nuclear fusion is the joining of two light nuclei to form a heavier nucleus.