Year 9 Science Semester Two Exam Revision: Electricity, Waves, and Energy Efficiency

Comprehensive vocabulary flashcards reviewing Year 9 Science Semester Two exam concepts covering Electricity (Chapter 9), Waves and Energy (Chapter 8), and Energy Efficiency (Chapter 10).

Electricity

The flow of electrical power or charge, typically through the movement of electrons along a conductor.

Electrical Conductor

A material that allows electric charges to flow freely and easily through it (such as copper wire).

Electrical Insulator

A material that tightly binds its electrons and strongly resists the flow of electric current (such as plastic or rubber).

Electric Circuit

A closed, continuous conducting path through which electric current can flow from a power source, through loads, and back.

Series Circuit

An electrical circuit configured with only a single pathway for current to travel through all connected components.

Parallel Circuit

An electrical circuit containing two or more separate branches, allowing current to divide so that each branch receives the full source voltage independently.

Voltage

The electrical potential difference between two points.

Electric Current

The rate at which electric charge flows past a point in a circuit, measured in amperes ($\text{A}$).

Electrical Resistance

The opposition to the flow of electric current offered by a material or component, measured in ohms ($\Omega$).

Ohm's Law

The physical law stating that current through a conductor between two points is directly proportional to voltage and inversely proportional to resistance, expressed as $V = I \times R$.

Static Electricity

The build-up of stationary electric charges on the surface of an object, typically caused by friction between two non-conducting materials.

Current Electricity

The controlled, continuous flow of electric charge through an electrical conductor within a circuit.

Voltmeter

An instrument connected in parallel across an electrical component to measure the potential difference (voltage) in volts ($\text{V}$).

Ammeter

An instrument connected in series within a circuit path to measure the rate of electric current flowing through it in amperes ($\text{A}$).

Direct Current (DC)

An electric current that flows continuously in one single direction only, typically supplied by batteries or power packs.

Alternating Current (AC)

An electric current that periodically reverses its direction of flow at regular intervals, commonly supplied by mains electricity.

Electrical Power

The rate at which electrical energy is transformed or consumed by an electrical device per unit time, calculated using the rule $P = V \times I$ and measured in watts ($\text{W}$).

Law of Conservation of Energy

A fundamental physical principle stating that energy cannot be created or destroyed; it can only be transformed from one form to another or transferred between objects.

Potential Energy

The stored energy an object possesses due to its position, state, or chemical composition (e.g., gravitational, elastic, or chemical energy).

Kinetic Energy

The form of energy an object possesses due to its motion.

Wave

A disturbance or oscillation that travels through a medium or space, transferring energy from one location to another without transferring matter.

Mechanical Wave

A wave that requires a physical substance or medium (such as a solid, liquid, or gas) to propagate, such as sound waves or water waves.

Electromagnetic Wave

A wave consisting of oscillating electric and magnetic fields that can propagate through a vacuum without requiring a physical medium (e.g., light waves or X-rays).

Longitudinal Wave

A wave in which the particles of the medium vibrate or oscillate parallel to the direction of wave travel and energy transfer.

Transverse Wave

A wave in which the particles of the medium oscillate perpendicular to the direction in which the wave and energy advance.

Compression

The region in a longitudinal wave where the particles or coils are closest together, corresponding to high pressure and density.

Rarefaction

The region in a longitudinal wave where the particles or coils are spread farthest apart, corresponding to low pressure and density.

Crest

The highest point or maximum positive displacement of a transverse wave above its equilibrium position.

Trough

The lowest point or maximum negative displacement of a transverse wave below its equilibrium position.

Amplitude

The maximum distance a particle is displaced from its central equilibrium position to either a crest or a trough.

Wavelength ($\lambda$)

The physical distance between two consecutive identical points on consecutive waves, such as crest-to-crest, trough-to-trough, or compression-to-compression.

Work

The measure of energy transferred when a force causes an object to move across a displacement, calculated using $\text{Work} = \text{Force} \times \text{Distance}$.

Conduction

The transfer of thermal energy between particles within a substance via direct contact and collisions without any bulk movement of the material.

Convection

The transfer of heat in fluids (liquids or gases) caused by the bulk movement of warmer, less dense fluid rising while cooler, denser fluid sinks.

Radiation (Thermal)

The transfer of thermal energy via electromagnetic waves (primarily infrared) that does not require matter or a medium to travel.

Period of a Wave

The time required for one full wave cycle to pass a fixed reference point, shown here completing one full cycle between $0\,\text{s}$ and $10\,\text{s}$ (Period = $10\,\text{s}$).

Frequency of a Wave ($f$)

The number of complete wave cycles that pass a given location per second, calculated as $f = \frac{\text{number of waves}}{\text{time}}$ and measured in hertz ($\text{Hz}$).

Pitch

The human perception of the frequency of a sound wave, where high frequencies correspond to high pitch and low frequencies correspond to low pitch.

Echo

A distinct repetition of a sound that is heard when sound waves reflect off a hard, distant boundary or surface back to the listener.

Law of Reflection

The optical principle stating that the angle of incidence ($i$) is strictly equal to the angle of reflection ($r$), both measured relative to the normal line.

Light Refraction

The bending of a light ray when it passes at an angle across a boundary from one transparent medium into another of differing density due to a change in propagation speed.

Convex Lens

A converging optical lens that is thicker at the centre than at the edges, refracting incoming parallel light rays inward to converge at a single focal point.

Concave Lens

A diverging optical lens that is thinner at the centre than at the edges, causing parallel rays of light to diverge outward away from a common axis.

Energy Efficiency

The proportion of total energy supplied to an appliance or machine that is converted into useful work or output, often represented as a decimal (e.g., $0.8$) or percentage ($80\%$).