Year 9 Physical Science: Energy, Waves, Light, Sound, and Generating Electricity

Comprehensive vocabulary revision flashcards covering energy forms, heat transfer, wave mechanics, sound, light, optics, and electricity generation.

Energy

The ability to exert a force and cause change, such as moving an object or altering its shape.

Potential Energy

Stored energy that, when released, can be converted into other forms such as sound, heat, or light energy (e.g., gravitational, elastic, chemical, or nuclear).

Kinetic Energy

The form of energy possessed by objects that are actively in motion.

Energy Transfer

The movement of energy from one object or system to another while remaining in the same form (e.g., kinetic energy passed from a cue ball to a pool ball).

Energy Transformation

The conversion of energy from one type into a different form (e.g., electrical energy transforming into light and heat inside a light bulb filament).

Heat Energy

The total kinetic energy of all individual particles making up an object, dependent on both particle speed and the total mass of matter present.

Temperature

A measurement proportional to the average kinetic energy of the particles within a substance.

Conduction

Heat transfer occurring via direct particle collisions, most effective in solids where closely packed particles vibrate and transfer kinetic energy along chemical bonds.

Convection

Heat transfer in fluids (liquids and gases) where heated particles spread out, become less dense, and float/rise, while cooler, denser fluid sinks.

Convection Current

The ongoing circular cycle of heat transfer in fluids where warmer fluid rises, moves away from the heat source, cools, increases in density, and sinks.

Radiation

The transfer of thermal energy via electromagnetic waves (radiant heat) that does not require the presence of particles and can travel across a vacuum.

Wave

A disturbance that transfers energy from one location to another through vibrations without causing a permanent transfer of matter.

Transverse Wave

A wave in which the particles or wave oscillations vibrate at right angles ($90^\circ$) to the direction of wave travel and energy transfer (e.g., light, ripples on water).

Longitudinal Wave

A wave in which the particles vibrate backward and forward parallel to the direction of energy propagation, creating alternating pulses of compression and rarefaction (e.g., sound).

Compression

A high-pressure region in a longitudinal wave where the transmitting medium's particles are forced closest together.

Rarefaction

A low-pressure region in a longitudinal wave where the transmitting medium's particles are spread furthest apart.

Wavelength

The physical distance between two consecutive matching points on a wave, such as between two peaks, two troughs, or two adjacent compressions; measured in metres ($\text{m}$).

Frequency

The number of complete wave cycles or vibrations passing a fixed point each second, measured in hertz ($\text{Hz}$).

Amplitude

The maximum displacement of a wave or vibrating particle from its rest (equilibrium) position, representing the amount of energy carried by the wave.

Sound Energy

A mechanical longitudinal compression wave produced by vibrating particles that requires a physical medium to travel and cannot propagate through a vacuum.

Pitch

The perceived highness or lowness of a sound, determined directly by the frequency of the sound wave (higher frequency corresponds to higher pitch).

Echo

The repetition of a sound caused by the reflection of a sound wave off a solid or liquid barrier back to the listener.

Echolocation

A biological navigation and hunting method used by animals such as bats and dolphins, in which high-frequency sound pulses are emitted and the returning echoes interpreted to locate objects.

Sonar

An underwater technology that transmits sound waves and measures their returning reflections to navigate, detect submerged hazards, or map the sea floor.

Ultrasound

Sound waves with frequencies above the upper limit of human hearing, used in medical diagnostic imaging by recording wave reflections at boundaries between different body tissues.

Electromagnetic Waves

Transverse waves composed of vibrating electric and magnetic fields that travel through a vacuum at approximately $300\,000\,000\,\text{m/s}$.

Radio Waves

The lowest-frequency, lowest-energy electromagnetic waves with the longest wavelengths, used primarily for communication (e.g., AM/FM radio, TV, emergency defence radio).

Microwaves

Electromagnetic waves that cause polar molecules to rotate rapidly and generate heat; widely used in cooking appliances, radar systems, and mobile phone data transmission.

Infrared Radiation

Electromagnetic radiation emitted by all warm objects and sensed as heat; utilized in thermal imaging, heat-detection systems, and satellite earth-temperature monitoring.

Visible Light

The narrow range of the electromagnetic spectrum that can be detected by the human retina, allowing visual perception.

Ultraviolet (UV) Radiation

Electromagnetic radiation just beyond visible violet light that stimulates vitamin D synthesis in human skin, but can cause sunburn and skin damage upon excessive exposure.

X-rays

High-energy electromagnetic radiation capable of passing through soft human tissue while being absorbed by denser bone and teeth, commonly used for radiography and radiation therapy.

Gamma Rays

The most energetic, highest-frequency electromagnetic waves produced during radioactive nuclear decay, utilized in targeted cancer treatments and nuclear processes.

Luminous

Describes an object that generates and radiates its own light (e.g., the Sun, flames, or an illuminated light bulb).

Ray

An idealized, narrow, straight-line trajectory showing the path taken by light energy (the path of a photon).

Beam

A stream or parallel group of many light rays travelling together.

Transparent

Describes a substance that allows almost all incident light to pass directly through without significant scattering, allowing objects behind to be viewed clearly.

Translucent

Describes a substance that transmits light partially while scattering it randomly, so that objects behind cannot be seen clearly.

Opaque

Describes a material that absorbs or reflects all incoming light, allowing none of it to pass through.

Law of Reflection

The optical principle stating that the angle of incidence equals the angle of reflection ($i = r$), measured relative to the normal line.

Normal

An imaginary reference line constructed perpendicular ($90^\circ$) to a reflective or refractive surface at the exact point where a light ray strikes.

Incident Ray

A ray of light originating from an emitter that approaches and hits a boundary or surface.

Reflected Ray

A ray of light that bounces off a surface after striking it.

Angle of Incidence

The angle formed between the incoming incident ray and the normal line.

Angle of Reflection

The angle formed between the outgoing reflected ray and the normal line.

Scattering

The diffuse reflection of light rays in many random directions upon striking an uneven or rough surface, preventing the formation of a distinct image.

Lateral Inversion

The sideways reversal effect observed in plane mirrors where the left and right sides of an object appear interchanged.

Concave Mirror

A mirror that curves inward like the inside of a bowl, causing parallel reflected rays to converge at a focal point and magnifying images when viewed close up.

Convex Mirror

A mirror that curves outward like the exterior of a sphere, causing reflected light rays to diverge and yielding an upright, reduced image across a wide viewing angle (e.g., security mirrors).

Refraction

The change in direction (bending) of a wave as it passes at an angle from one medium into another of different optical density, caused by a change in wave speed.

Refractive Index

A dimensionless physical measurement ($n$) describing how much a medium slows down and refracts light compared to the speed of light in a vacuum.

Angle of Refraction

The angle formed between the refracted light ray traveling through a second medium and the normal line.

Convex Lens (Biconvex)

A converging lens that is thicker at the centre than at the edges, causing passing parallel light rays to bend inward and converge at a real focal point (e.g., magnifying glasses).

Concave Lens (Diverging)

A lens that is thinner at the centre than at the perimeter, causing parallel light rays passing through to spread outward so that they trace back to a virtual focal point.

Focal Point

The common intersection point where converging rays of light meet (or from which diverging rays appear to emanate) after interacting with a curved lens or mirror.

Focal Length

The linear distance along the principal optical axis from the central plane of a lens or mirror surface to its focal point.

Electric Generator

A device that converts mechanical kinetic energy into electrical energy by utilizing relative physical movement between a coil of wire and an external magnetic field.

Turbine

A mechanical assembly consisting of rotating blades driven by fluid flow (steam, wind, water, or gas) to rotate a generator shaft and generate electricity.

Direct Current (DC)

An electric current that maintains a continuous flow in only one direction through a circuit with fixed positive and negative voltage polarity (e.g., batteries and solar cells).

Alternating Current (AC)

An electric current whose charges continually switch directions back and forth along a conductor approximately $100$ times per second, characterized by alternating positive and negative terminals.

Loy Yang A Power Station

A major thermal power station situated in the Latrobe Valley of Melbourne's East that burns coal to produce electricity for the Victorian grid.