Key definitions

AQA 8463 · 8463 mark-scheme terms

The quantities and laws AQA marks to the word across all eight 8463 topic areas — energy, electricity, particles, atomic structure, forces, waves, magnetism and space physics.

Reading mode — read across, know each one cold.

Term	Mark-scheme definition
Scalar quantity	A quantity that has magnitude (size) only.e.g. speed, distance, mass, energy, temperature.
Vector quantity	A quantity that has both magnitude and direction.e.g. velocity, displacement, force, acceleration, momentum.
Displacement	The straight-line distance from an object's starting point to its finishing point, in a stated direction (a vector).
Speed	The distance travelled per unit time (a scalar).
Velocity	The speed of an object in a given direction (a vector).
Acceleration	The change in velocity per unit time.
Mass	The amount of matter in an object (measured in kg).
Weight	The force acting on an object due to gravity (W = m g); measured in newtons.
Gravitational field strength (g)	The force per unit mass acting on an object (N/kg).
Resultant force	The single force that has the same effect as all the forces acting on an object added together.
Newton's First Law	If the resultant force on an object is zero, a stationary object stays still and a moving object keeps moving at a constant velocity.
Newton's Second Law	The acceleration of an object is proportional to the resultant force and inversely proportional to its mass (F = m a).
Newton's Third Law	When two objects interact, they exert equal and opposite forces on each other.
Work done	The energy transferred when a force moves an object through a distance (W = F s).1 joule of work is done when a force of 1 newton moves an object 1 metre.
Power	The rate of energy transfer, or the rate of doing work.1 watt = 1 joule per second.
Efficiency	(Useful output energy transfer / total input energy transfer) — multiply by 100 for a percentage.
Momentum	Mass x velocity (p = m v); a vector, measured in kg m/s.
Conservation of momentum	In a closed system, the total momentum before an event equals the total momentum after it.
Density	The mass per unit volume of a substance.density = mass / volume; unit kg/m³.
Limit of proportionality	The point beyond which extension is no longer directly proportional to the force applied.
Terminal velocity	The constant velocity reached when the resultant force is zero because the resistive force equals the object's weight.
Hooke's Law	The extension of an elastic object is directly proportional to the force applied, provided the limit of proportionality is not exceeded.
Potential difference	The energy transferred (work done) per unit charge passing between two points.1 volt = 1 joule per coulomb.
Electric current	The rate of flow of electric charge.current = charge flow / time.
Resistance	The opposition to the flow of charge; the ratio of potential difference to current.
Specific heat capacity	The energy needed to raise the temperature of 1 kg of a substance by 1 degree Celsius.
Specific latent heat	The energy needed to change the state of 1 kg of a substance with no change in temperature.
Wave	A disturbance that transfers energy from one place to another without transferring matter.
Transverse wave	A wave in which the oscillations are perpendicular to the direction of energy transfer.e.g. electromagnetic waves, ripples on water.
Longitudinal wave	A wave in which the oscillations are parallel to the direction of energy transfer.e.g. sound waves — shown as compressions and rarefactions.
Frequency	The number of waves passing a point per second (Hz).
Wavelength	The distance from one point on a wave to the equivalent point on the next wave.
Amplitude	The maximum displacement of a point on a wave from its undisturbed (rest) position.
Period	The time taken for one complete wave to pass a point (T = 1 / f).
Refraction	The change in direction of a wave as it changes speed when crossing a boundary between two media.
Radioactive decay	The random process by which an unstable nucleus emits radiation to become more stable.
Activity	The rate at which unstable nuclei in a source decay.Measured in becquerels (Bq); 1 Bq is 1 decay per second.
Count rate	The number of ionising-radiation events detected per unit time.
Irradiation	Exposing an object to ionising radiation; the object does not become radioactive.
Contamination	The unwanted presence of radioactive atoms on or inside an object.
Half-life	The time taken for the number of unstable nuclei in a sample (or the count rate) to halve.
Nuclear fission	The splitting of a large, unstable nucleus into two smaller nuclei, releasing energy and neutrons.
Nuclear fusion	The joining of two small nuclei to form a larger nucleus, releasing energy.
Renewable energy resource	A resource that is replenished as fast as it is used, so it will not run out.
Magnetic field	A region where a magnetic material, magnet or current-carrying conductor experiences a force.
Electromagnet	A magnet produced by an electric current, whose field can be switched on and off.
Motor effect	The force produced when a current-carrying conductor is placed in a magnetic field.
Red-shift	An increase in the observed wavelength of light from an object moving away from the observer.
Light-year	The distance travelled by light through a vacuum in one year.
Orbit	A curved path in which gravity provides the force that continually changes an object's velocity.

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