GCE A/L Science for Technology key terms

One of the seven fundamental units of the International System (metre, kilogram, second, ampere, kelvin, mole, candela) from which all other units are derived by multiplication and division.

A unit formed by combining base units, such as the newton (kg m s⁻²) or the watt (kg m² s⁻³), used to express quantities that are not fundamental.

A method of checking equations and converting units by comparing the base dimensions of each term, since both sides of a valid equation must have identical dimensions.

The digits in a measurement that carry real information about its precision, including one estimated digit; the result of a calculation should not be quoted beyond the precision of its inputs.

The difference between a measured value and the accepted value, expressed as a percentage of the accepted value, used to judge the accuracy of an experiment.

A consistent deviation in the same direction caused by faulty instruments, zero errors or poor technique; it shifts all readings and is not reduced by repeating measurements.

Unpredictable scatter in readings arising from limitations of the observer or instrument; it can be reduced by taking multiple readings and calculating a mean.

The turning effect of a force about a pivot, calculated as force multiplied by the perpendicular distance from the pivot to the line of action of the force, measured in newton metres.

The single point through which the entire weight of a body may be considered to act, important for analysing stability and toppling in structures and machines.

The state of a body when the net force and net moment acting on it are both zero, so it remains at rest or moves with constant velocity.

The ratio of tensile stress to tensile strain in the linear region of a stress–strain graph, a measure of the stiffness of a material measured in pascals.

Stress is force per unit cross-sectional area (Pa); strain is the fractional change in length (no units). Their ratio gives the stiffness of a material.

The greatest stress a material can withstand and still return to its original shape when the load is removed; beyond it, permanent deformation occurs.

The rotational effect of a force about an axis, equal to force times perpendicular distance, or for a coil, the product of magnetic flux density, current, area and number of turns.

The energy required to raise the temperature of one kilogram of a substance by one kelvin, measured in J kg⁻¹ K⁻¹ and used in calorimetry calculations.

The energy absorbed or released when a substance changes state at constant temperature, without any change in temperature; specific latent heat is quoted per kilogram.

A property describing how readily a material conducts heat, defined by the rate of heat flow per unit area per unit temperature gradient, measured in W m⁻¹ K⁻¹.

Heat transfer by the bulk movement of a fluid, where warmer, less dense fluid rises and cooler, denser fluid sinks, setting up circulation currents.

The change of a liquid to vapour at its surface at any temperature, taking latent heat from the surroundings and causing cooling.

The change in direction of a wave as it passes from one medium to another of different optical density, caused by a change in wave speed.

The ratio of the speed of light in a vacuum to its speed in a medium, determining how much a ray bends at a boundary between two media.

The complete reflection of light inside a denser medium when the angle of incidence exceeds the critical angle; the basis of optical fibres and some prisms.

A large increase in amplitude when a system is driven at its natural frequency, important in acoustics, tuning circuits and the design of structures to avoid vibration damage.

A stationary pattern of nodes and antinodes formed when two waves of equal frequency and amplitude travel in opposite directions and superpose.

Two rules for circuits: the total current entering a junction equals the total leaving it, and the sum of potential differences around any closed loop is zero.

The resistance within a source of emf that causes the terminal voltage to fall below the emf when current is drawn, dissipating energy as heat inside the source.

A circuit of two or more resistors in series across a supply, used to obtain a fraction of the supply voltage across one component.

The generation of an emf in a conductor whenever the magnetic flux linking it changes, described by Faraday's law and used in generators and transformers.

A device with two coils on a shared magnetic core that changes alternating voltage; the voltage ratio equals the turns ratio, and power is conserved ideally.

The strong electrostatic attraction between oppositely charged ions formed when one atom transfers electrons to another, typically between a metal and a non-metal.

A bond formed when two atoms share one or more pairs of electrons, giving strong directional bonds typical of non-metal compounds and organic molecules.

A measure of the tendency of an atom in a molecule to attract a shared pair of electrons towards itself, increasing across a period and decreasing down a group.

One of two or more compounds with the same molecular formula but different arrangements of atoms, giving different physical and chemical properties.

An atom or group of atoms within a molecule that determines its characteristic chemical reactions, such as hydroxyl, carboxyl, amino or ester groups.

A reaction in which unsaturated monomers join repeatedly through their double bonds to form a long chain polymer without eliminating any small molecule.

A protein catalyst that speeds up a specific biochemical reaction by lowering its activation energy, and whose activity depends on temperature and pH.

The net movement of water molecules through a partially permeable membrane from a region of higher water potential to one of lower water potential.

The type of cell division producing two genetically identical daughter cells with the same chromosome number as the parent, responsible for growth and repair.

A reduction division producing four haploid gametes with half the chromosome number, involving crossing over and independent assortment to create genetic variation.

One of the alternative versions of a gene occupying the same locus on a chromosome, which may be dominant or recessive in its expression.

The process by which chlorophyll-containing plants use light energy to convert carbon dioxide and water into glucose and oxygen, storing energy in chemical bonds.

The loss of water vapour from the leaves of plants through stomata, which pulls water up the xylem and cools the plant.

A biotechnology technique in which small pieces of plant or animal tissue are grown on a sterile nutrient medium to produce many genetically identical individuals.

The process of comparing an instrument's readings with a known standard and adjusting it so that measurements are accurate and traceable.

A device that converts one form of energy into another, such as a thermistor converting temperature change into a resistance change for measurement or control.

A control strategy in which the output is measured and compared with a set value, and the difference is used to adjust the input to keep the system stable.