Paper 1 Definitions

Alpha Decay

The process of an unstable nucleus emitting an alpha particle (two protons and two neutrons) to become more stable.

Annihilation

The process of a particle and its antiparticle colliding and being converted into energy.

Antiparticle

A corresponding particle with the same mass but opposite charge and conservation numbers.

Baryon Number

A quantum number that is conserved in all particle interactions, where baryons have a baryon number of +1.

Baryon

A class of hadron made up of three quarks; the proton is the only stable baryon.

Beta-Minus Decay

The process of a neutron turning into a proton, emitting a beta-minus particle (an electron) and an antineutrino.

Beta-Plus Decay

The process of a proton turning into a neutron, emitting a beta-plus particle (a positron) and a neutrino.

Electron Diffraction

The spreading of electrons as they pass through a gap similar to the magnitude of their de Broglie wavelength.

Electron-volt (eV)

Work done to accelerate an electron through a potential difference of 1V.

Energy Levels

Defined energies at which electrons can exist in an atom; electrons cannot exist between levels.

Excitation

The process of an electron taking in energy to move to a higher energy level.

Gauge Boson

Exchange particles that transmit the four fundamental interactions between particles.

Ground State

The most stable energy level that an electron can exist in.

Hadrons

A class of particles that experiences the strong nuclear interaction.

Ionisation

The process of an atom losing an orbital electron and becoming charged.

Isotope

Atoms with the same number of protons but different numbers of neutrons.

Isotopic Data

Data from isotopes used for purposes like carbon dating.

Kaon

A type of meson that decays into pions.

Lepton Number

A quantum number conserved in all particle interactions.

Lepton

Elementary subatomic particles, including electrons, muons, and neutrinos.

Meson

A class of hadron made up of a quark and an antiquark pair.

Muon

A type of lepton that decays into electrons.

Neutrino

A subatomic particle hypothesized to maintain the conservation of energy in beta decay.

Nucleon Number (A)

The sum of protons and neutrons in a nucleus.

Nucleon

A proton or neutron.

Pair Production

The process of a high-energy photon converting into a particle and its antiparticle.

Photon

A packet of energy.

Pion

A type of meson and the exchange particle for the strong nuclear force.

Positron

The antiparticle of an electron with a positive charge.

Proton Number (Z)

The number of protons in the nucleus of an element.

Stopping Potential

The minimum potential difference required to stop the highest energy electrons in the photoelectric effect.

Strange Particles

Particles produced through the strong interaction but decay via the weak interaction.

Strangeness

A quantum number conserved in strong interactions but not in weak interactions.

Strong Nuclear Force

Force that acts between nucleons to keep the nucleus stable.

Threshold Frequency

The minimum frequency needed for photoelectrons to be emitted from a metal plate.

Work Function

The minimum energy required to remove an electron from a metal’s surface.

Amplitude

A wave’s maximum displacement from its equilibrium position.

Antinode

A position of maximum displacement in a stationary wave.

Cladding

A protective layer on optical fibre to improve strength and prevent signal transfer.

Coherence

Waves with the same wavelength and frequency and a fixed phase difference.

Diffraction Grating

A device with hundreds of slits per millimetre used to analyze elements.

Diffraction

The spreading of waves as they pass through a gap of similar magnitude to their wavelength.

Electromagnetic Waves

Waves consisting of perpendicular electric and magnetic oscillations.

Frequency

The number of waves that pass a point in a unit time period.

Fringe Spacing

The distance between two adjacent bright or dark fringes.

Interference

Superposition of waves when two waves meet.

Laser

A light source that produces a coherent beam.

Longitudinal Wave

A wave with oscillations parallel to the direction of energy propagation.

Material Dispersion

Different wavelengths traveling at different speeds through optical fibre.

Modal Dispersion

Different angles of waves entering an optical fibre causing pulse broadening.

Node

A position of minimum displacement in a stationary wave.

Optical Fibre

A thin glass fibre through which signals are passed.

Path Difference

How far ahead one wave is compared to another, usually in terms of wavelength.

Phase Difference

Difference in phase between two points on a wave.

Phase

How far through the wave’s cycle a point is.

Polarisation

Restriction of a wave to oscillate in a single plane.

Pulse Broadening

Elongation of a signal down an optical fibre due to dispersion.

Refractive Index

Ratio of speed of light in a vacuum to speed in a given material.

Snell’s Law

Links a wave's angle of incidence to its angle of refraction using refractive indexes.

Wave Speed

The product of a wave’s frequency and wavelength.

Stationary Wave

A wave that stores energy but does not transfer it.

Total Internal Reflection

Full reflection occurs at the inside boundary of an optical fibre.

Transverse Wave

A wave with oscillations perpendicular to the direction of energy propagation.

Wavelength

Distance between two identical positions on adjacent waves.

Young’s Double-Slit Experiment

Experiment demonstrating diffraction of light through two narrow slits.

Breaking Stress

The maximum stress an object can withstand before failure.

Brittle

An object that shows little strain before reaching breaking stress.

Centre of Mass

The single point through which all mass of an object acts.

Conservation of Energy

Energy cannot be created or destroyed; it can only change forms.

Conservation of Momentum

Total momentum of a system remains constant without external forces.

Couple

Two equal and opposite parallel forces causing rotation without translation.

Density

Mass per unit volume of a material.

Efficiency

Ratio of useful output to total input for a system.

Elastic Behaviour

Material returns to original shape when deforming forces are removed.

Elastic Collision

Total kinetic energy before and after collision remains the same.

Elastic Limit

Force beyond which an object will not return to its original shape.

Elastic Strain Energy

Energy stored when an object is stretched.

Equilibrium

Condition where resultant force and moment are zero.

Hooke’s Law

Extension of an elastic object is proportional to the force applied.

Impulse

Change of momentum of an object when a force acts on it.

Inelastic Collision

Total kinetic energy changes before and after a collision.

Moment

The product of force and the perpendicular distance to the pivot.

Momentum

Product of mass and velocity of an object.

Newton’s First Law

An object remains in its state of motion unless acted on by a force.

Newton’s Second Law

Sum of forces equals the rate of change of momentum.

Newton’s Third Law

For every action, there is an equal and opposite reaction.

Plastic Behaviour

Material does not return to its original shape after deformation.

Principle of Moments

Sum of clockwise moments equal to sum of anticlockwise moments for equilibrium.

Scalar

A quantity with only magnitude; examples include length and mass.

Spring Constant

Constant of proportionality for spring extension under force.

Stiffness

Measure of difficulty in stretching an object.

Tensile Strain

The ratio of extension to original length; unitless.

Tensile Stress

Force acting per unit area; measured in Pascals.

Terminal Speed

Maximum speed when resistive and driving forces balance each other.

Vector

A quantity with both magnitude and direction.

Young Modulus

Ratio of stress to strain for a given material.

Ammeter

Device measuring current in a circuit when connected in series.

Current

Rate of flow of charge in a circuit.

Electromotive Force

Energy transferred by a source to each unit charge passing through.

Internal Resistance

Resistance to charge flow within a source.