Cambridge IGCSE™ Physics 0625 Vocabulary Review

A comprehensive collection of vocabulary terms, formulas, and definitions from the Cambridge IGCSE Physics 0625 syllabus for the 2023-2025 examinations.

Scalar quantity

A quantity that has magnitude (size) only, such as distance, speed, time, mass, energy, and temperature.

Vector quantity

A quantity that has both magnitude and direction, such as force, weight, velocity, acceleration, momentum, electric field strength, and gravitational field strength.

Speed

The distance travelled per unit time, calculated using the equation $v = \frac{s}{t}$.

Velocity

Speed in a given direction.

Acceleration

The change in velocity per unit time, calculated using the equation $a = \frac{\Delta v}{\Delta t}$.

Acceleration of free fall ($g$)

For an object near the surface of the Earth, it is approximately constant at $9.8\,m/s^2$.

Mass

A measure of the quantity of matter in an object at rest relative to the observer.

Weight

A gravitational force on an object that has mass, defined as the effect of a gravitational field on a mass.

Gravitational field strength ($g$)

The force per unit mass, calculated using the equation $g = \frac{W}{m}$.

Density

Mass per unit volume, calculated using the equation $\rho = \frac{m}{V}$.

Spring constant ($k$)

Force per unit extension, calculated using the equation $k = \frac{F}{x}$.

Limit of proportionality

The point on a load-extension graph beyond which the extension is no longer proportional to the load.

Resultant force ($F$)

The single force that determines acceleration via the equation $F = ma$, where force and acceleration are in the same direction.

Solid friction

The force between two surfaces that may impede motion and produce heating.

Moment

A measure of the turning effect of a force, calculated as $moment = force \times \text{perpendicular distance from the pivot}$.

Equilibrium

A state in which there is no resultant force and no resultant moment on an object.

Centre of gravity

The point on an object through which its whole weight acts.

Momentum ($p$)

The product of mass and velocity, calculated as $p = mv$.

Impulse

The product of force and the time for which the force acts, calculated as $impulse = F\Delta t = \Delta (mv)$.

Conservation of energy

A principle stating that energy might be stored or transferred but cannot be created or destroyed.

Efficiency

The ratio of useful output to total input, calculated by $\frac{\text{useful energy output}}{\text{total energy input}} \times 100\%$ or $\frac{\text{useful power output}}{\text{total power input}} \times 100\%$.

Work ($W$)

Mechanical work done when a force moves an object, calculated as $W = Fd = \Delta E$.

Power ($P$)

Work done per unit time or energy transferred per unit time, calculated as $P = \frac{W}{t}$ or $P = \frac{\Delta E}{t}$.

Pressure ($p$)

Force per unit area, calculated as $p = \frac{F}{A}$; for liquids, the change in pressure is $\Delta p = \rho g\Delta h$.

Absolute zero

The lowest possible temperature ($-273^{\circ}C$) where particles have the least kinetic energy.

Brownian motion

The random motion of microscopic particles in a suspension resulting from random collisions with light, fast-moving molecules.

Specific heat capacity ($c$)

The energy required per unit mass per unit temperature increase, calculated as $c = \frac{\Delta E}{m\Delta \theta}$.

Conduction

Thermal energy transfer in solids through atomic or molecular lattice vibrations and the movement of delocalised electrons.

Convection

Thermal energy transfer in liquids and gases resulting from density changes.

Transverse wave

A wave where the direction of vibration is at right angles to the direction of propagation, such as electromagnetic radiation.

Longitudinal wave

A wave where the direction of vibration is parallel to the direction of propagation, such as sound waves.

Refractive index ($n$)

The ratio of the speeds of a wave in two different regions, calculated as $n = \frac{\sin(i)}{\sin(r)}$.

Critical angle ($c$)

The angle of incidence above which total internal reflection occurs, related to refractive index by $n = \frac{1}{\sin(c)}$.

Monochromatic

Visible light of a single frequency.

Ultrasound

Sound with a frequency higher than $20\,kHz$.

Induced magnetism

The phenomenon where a magnetic material becomes a magnet when placed in a magnetic field.

Electric field

A region in which an electric charge experiences a force.

Electric current ($I$)

The charge passing a point per unit time ($I = \frac{Q}{t}$), measured in Amperes ($A$).

Electromotive force (e.m.f.)

The electrical work done by a source in moving a unit charge around a complete circuit.

Potential difference (p.d.)

The work done by a unit charge passing through a component.

Resistance ($R$)

The ratio of potential difference to current, calculated by $R = \frac{V}{I}$ and measured in Ohms ($\Omega$).

Kilowatt-hour (kWh)

A unit of energy used for billing electrical appliances.

Electromagnetic induction

The process where a conductor moving across a magnetic field induces an e.m.f. in the conductor.

Proton number ($Z$)

The number of protons in the nucleus of an atom, also known as the atomic number.

Nucleon number ($A$)

The total number of protons and neutrons in the nucleus of an atom, also known as the mass number.

Isotope

Atoms of the same element that have the same number of protons but different numbers of neutrons.

Nuclear fission

The process of splitting a nucleus into smaller parts.

Nuclear fusion

The process of joining nuclei together, which occurs in the Sun and powers stars.

Half-life

The time taken for half the nuclei of a particular isotope in a sample to decay.

Light-year

The distance travelled in a vacuum by light in one year, approximately $9.5 \times 10^{15}\,m$.

Redshift

An increase in the observed wavelength of electromagnetic radiation emitted from receding stars and galaxies.

Hubble constant ($H_0$)

The ratio of the speed at which a galaxy is moving away from Earth to its distance ($H_0 = \frac{v}{d}$), estimated at $2.2 \times 10^{-18}\,s^{-1}$.

Cosmic microwave background radiation (CMBR)

Microwave radiation observed at all points in space, produced shortly after the Universe was formed.

Accuracy

How close a measurement result is to the true value.

Precision

How close the measured values of a quantity are to each other.