Physics Module 4: Definitions

Conductors

A material that allows the flow of electrical charge; good conductors have many free charge carriers.

Conservation of Charge

The total charge in a system cannot change.

Conventional Current

The direction of current defined as flow from positive to negative.

Coulomb

The SI unit of electric charge.

Electric Current

The rate of flow of charge in a circuit.

Electrolytes

Substances containing ions that act as charge carriers when dissolved, allowing current to flow.

Electron Flow

The actual flow of electrons from negative to positive (opposite to conventional current).

Elementary Charge

The smallest unit of charge; the magnitude of an electron's charge.

Insulators

Materials with no free charge carriers that do not allow charge to flow.

Kirchhoff's First Law

At a junction, the total current entering equals the total current leaving.

Mean Drift Velocity

The average velocity of charge carriers in a conductor; proportional to current and inversely proportional to carrier density and cross-sectional area.

Quantisation of Charge

Charge exists only in discrete multiples of the elementary charge.

Semiconductors

Materials whose number of charge carriers (and thus conductivity) can change; examples include light-dependent resistors and thermistors.

Diode

A component that allows current in one direction only; requires a threshold forward voltage to conduct.

Electromotive Force

Energy supplied by a source per unit charge (measured in volts).

Filament Lamp

A bulb with a metal filament that glows when heated; its resistance increases with temperature.

I-V Characteristics

Plots of current versus voltage showing how components behave.

Kilowatt-Hour

A unit of electrical energy commonly used for domestic consumption (kW·h).

Light-Dependent Resistor

A light-sensitive semiconductor whose resistance decreases as light intensity increases.

Negative Temperature Coefficient Thermistor

A thermistor whose resistance decreases as temperature increases.

Ohm

The SI unit of electrical resistance (Ω).

Ohmic Conductor

A conductor for which current is directly proportional to potential difference under constant conditions.

Ohm's Law

For an ohmic conductor, V = I * R.

Potential Difference

Work done per unit charge to move a charge between two points; measured in volts.

Power

The rate of energy transfer; P = I * V.

Resistance

A measure of how difficult it is for current to flow through a material.

Resistivity

A material property relating resistance to geometry: R = rho * (length / area).

Resistor

A device with a fixed resistance that follows Ohm's law.

Volt

The SI unit of potential difference (V).

Conservation of Energy

Energy cannot be created or destroyed; it can only be transferred or converted.

Internal Resistance

Resistance inside a source that causes energy loss and reduces terminal voltage.

Kirchhoff's Second Law

The sum of the voltages around any closed loop equals zero.

Lost Volts

The difference between a source's emf and its terminal voltage; the voltage dropped across internal resistance.

Parallel Circuit

Components connected across the same two points so each has the same potential difference.

Potential Divider

Two resistors in series used to split a potential difference in the ratio of their resistances.

Resistors in Parallel

Resistors sharing the same potential difference; total resistance given by 1/R_total = 1/R1 + 1/R2 + ….

Resistors in Series

Resistors with the same current; total resistance is the sum of individual resistances.

Sensor Circuits

Circuits that respond to external conditions, often using a semiconductor in a potential divider.

Series Circuit

Components connected end-to-end in one loop so the same current flows through each.

Terminal PD

The potential difference across a source's terminals; equal to emf minus lost volts.

Amplitude

The maximum displacement of a wave from its equilibrium position.

Antinodes

Positions of maximum displacement in a stationary wave.

Coherence

Waves having the same frequency and a constant phase difference.

Constructive Interference

When waves meet in phase and their amplitudes add.

Critical Angle

The angle of incidence that gives a refracted angle of 90 degrees; beyond this total internal reflection occurs.

Destructive Interference

When waves meet in antiphase and their amplitudes cancel.

Diffraction

The spreading of waves when they pass through a gap comparable to their wavelength.

Displacement

The distance of a point on a wave from its equilibrium position.

Electromagnetic Spectrum

The range of EM waves: gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, radio waves.

Electromagnetic Waves

Perpendicular electric and magnetic oscillations that travel at the speed of light in a vacuum.

Frequency

The number of wave cycles per unit time; f = 1 / period.

Fundamental Mode of Vibration

The lowest-frequency standing-wave pattern (natural frequency).

Intensity

Power transferred per unit area; proportional to amplitude squared.

Interference

The superposition of two or more waves producing a resultant displacement.

Longitudinal Waves

Waves with oscillations parallel to propagation (e.g., sound); cannot travel in a vacuum.

Nodes

Positions of zero displacement in a stationary wave.

Oscilloscope

A device for displaying and analysing waveforms.

Path Difference

The difference in distance travelled by two waves, often expressed in wavelengths.

Period

The time for one complete wave cycle.

Phase Difference

The difference in phase between two points on a wave, usually in radians.

Polarisation

Restriction of a transverse wave to oscillate in a single plane.

Progressive Waves

Waves that transfer energy from one place to another without transferring matter.

Reflection

When a wave bounces at a boundary; angle of incidence equals angle of reflection.

Refraction

Change in wave speed and direction when entering a new medium; waves slow in optically denser media.

Refractive Index

n = (speed of light in vacuum) / (speed of light in material).

Stationary Wave

A wave pattern that stores energy but does not transfer it along the medium.

Superposition

When waves meet, the total displacement is the sum of individual displacements.

Total Internal Reflection

Complete internal reflection at an internal boundary when incidence angle exceeds the critical angle; used in optical fibres.

Transverse Waves

Waves with oscillations perpendicular to the direction of propagation (e.g., electromagnetic waves).

Wave Speed

v = f * lambda.

Wavelength

The distance between identical points on adjacent waves (e.g., peak to peak).

Young Double-Slit Experiment

An experiment showing interference and diffraction of monochromatic light through two narrow slits producing bright and dark fringes.

Atom Spacing

The distance between adjacent atoms in a crystal lattice, important in electron diffraction.

de Broglie Equation

Relates particle wavelength to momentum: lambda = h / p.

Diffraction (Electron Diffraction)

The bending and spreading of electrons through narrow slits or around obstacles, showing wave-like behaviour.

Electron Diffraction

Observation of electrons displaying wave-like behaviour when passing through thin materials such as polycrystalline graphite.

Electronvolt (eV)

Energy gained by an electron accelerated through 1 volt: 1 eV = 1.6 x 10^-19 J.

Photon

A quantum (packet) of electromagnetic energy exhibiting both particle and wave properties.

Photon Model

A model treating light as discrete photons, explaining effects like the photoelectric effect.

Photon Energy

E = h * f.

Photoelectric Effect

Emission of electrons from a metal when illuminated by radiation above a threshold frequency, showing light's particle nature.

Photoelectric Equation

h * f = phi + KE_max (photon energy = work function + maximum kinetic energy of emitted electrons).

Planck Constant (h)

Fundamental constant relating energy and frequency: h = 6.63 x 10^-34 J s.

Threshold Frequency

The minimum frequency of incident radiation required to eject electrons from a material.

Wave-Particle Duality

The principle that particles exhibit both wave-like and particle-like properties.

Work Function

phi: the minimum energy required to remove an electron from a metal surfac