BGCSE Physics 1427 key terms

The straight-line distance and direction from a starting point to a finishing point; a vector quantity, so it differs from the total distance travelled along a path.

The rate at which displacement changes with time, including direction. It is a vector quantity measured in metres per second, and it differs from speed because direction matters.

The rate of change of velocity with time, measured in metres per second squared; an object accelerates when it speeds up, slows down or changes direction.

The single force that has the same effect as all the forces acting on a body combined; an unbalanced resultant force causes acceleration in its direction.

The turning effect of a force, equal to the force multiplied by the perpendicular distance from the pivot to the line of action of the force.

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

Energy transferred when a force moves an object along its line of action, calculated as force multiplied by distance moved in the direction of the force, measured in joules.

The energy a body possesses because of its motion, equal to half its mass multiplied by the square of its speed, measured in joules.

The rate at which energy is transferred or work is done, equal to energy transferred divided by time taken, measured in watts; one watt equals one joule per second.

The ratio of useful energy or power output to total energy or power input, usually expressed as a percentage; no real machine is one hundred percent efficient.

The rate of flow of electric charge past a point in a circuit, measured in amperes; one ampere is one coulomb of charge passing per second.

The energy transferred per unit charge between two points in a circuit, measured in volts; one volt is one joule per coulomb of charge moved.

A measure of how difficult it is for current to flow through a component, equal to potential difference divided by current, measured in ohms.

For a conductor kept at constant temperature, the current through it is directly proportional to the potential difference across it, so its resistance stays constant.

A circuit in which components are connected one after another so the same current flows through each, while the supply voltage is shared between them.

A circuit in which components are connected across the same two points, so each receives the full supply voltage and the current splits between the branches.

The rate at which electrical energy is transferred by a component, equal to voltage multiplied by current, or to current squared multiplied by resistance.

The production of a potential difference in a conductor when it experiences a changing magnetic field, or when it moves through a magnetic field.

The maximum displacement of a point on a wave from its rest or equilibrium position; the larger the amplitude, the more energy the wave carries.

The distance between two consecutive corresponding points on a wave, such as from one crest to the next, measured in metres.

The number of complete waves passing a fixed point each second, measured in hertz; it equals one divided by the period of the wave.

The distance a wave crest travels each second through a medium, calculated as frequency multiplied by wavelength and measured in metres per second.

The change in direction of a wave as it passes from one medium into another where its speed is different, caused by a change in wave speed.

The complete reflection of light inside a denser medium when it strikes the boundary at an angle greater than the critical angle, used in optical fibres.

An image formed where light rays actually meet after passing through a lens or reflecting from a mirror; it can be projected onto a screen.

A wave in which particles of the medium vibrate parallel to the direction in which the wave travels, such as sound, forming compressions and rarefactions.

The energy needed to raise the temperature of one kilogram of a substance by one degree Celsius, measured in joules per kilogram per degree Celsius.

The energy needed to change one kilogram of a substance from one state to another at its melting or boiling point, with no change in temperature.

The transfer of heat through a solid by particles vibrating and passing energy to neighbouring particles, without the material itself moving from place to place.

The transfer of heat in fluids by the movement of warmer, less dense regions rising and cooler, denser regions sinking, forming convection currents.

The increase in size of a substance when heated, because its particles vibrate more and move slightly further apart on average.

The number of protons in the nucleus of an atom, which identifies the element and equals the number of electrons in a neutral atom.

Atoms of the same element with the same number of protons but different numbers of neutrons, so they have different mass numbers and masses.

The time taken for half of the radioactive nuclei in a sample to decay, or for the count rate from a source to fall to half its initial value.

A helium nucleus consisting of two protons and two neutrons, emitted during radioactive decay; it is highly ionising and stopped by a sheet of paper.

How close a measured value is to the true or accepted value; accurate results have small errors overall and are judged against a reliable reference.

An error that shifts every reading in the same direction by a similar amount, often caused by a zero error or faulty calibration of the instrument.

An error that varies unpredictably between repeat readings, caused by factors such as reaction time or fluctuating conditions; it is reduced by averaging repeats.

The range within which the true value of a measurement is likely to lie, often stated as plus or minus half the smallest scale division.