Year 9 Science: Physics Revision - Energy, Waves, Light, and Sound

Comprehensive vocabulary flashcards covering Year 9 Physics topics including forms of energy, heat transfer mechanisms, light properties, reflection, refraction, eye anatomy, and sound wave properties.

Energy

The potential to do work (make things happen), measured in Joules ($J$).

Active Energy

A category of energy whose effects are readily seen or detected, such as heat, kinetic, sound, and electrical energy.

Potential Energy

Stored energy that only displays an effect once it is transformed into an active form of energy, such as gravitational, chemical, or elastic potential energy.

Law of Conservation of Energy

A fundamental scientific law stating that energy cannot be created or destroyed, only transformed from one form to another or transferred between objects.

Energy Efficiency

The percentage of input energy that is converted into useful output energy rather than being wasted as heat or other non-useful forms.

Heat Energy (Thermal Energy)

The total kinetic energy of all the vibrating particles contained within an object or substance.

Temperature

A measure of the average kinetic energy of the individual particles that make up an object.

Conduction

The process of heat transfer occurring primarily in solids (especially metals), where vibrating particles collide with neighbouring particles and pass vibrations along.

Convection

The transfer of heat energy occurring in liquids and gases caused by the bulk movement of fluid particles, where warmer fluid expands, becomes less dense, and rises.

Convection Current

The continuous cyclical flow formed when warm, less dense fluid rises and cooler, denser fluid sinks to take its place.

Infrared Radiation

Electromagnetic waves emitted by warm objects that transfer heat energy without requiring particles, allowing them to travel through gases and a vacuum.

Thermal Insulator

A material, such as plastic or air, that conducts heat poorly and resists the transfer of thermal energy.

Wave

A disturbance that transmits energy from one point to another without the transmittance of matter.

Electromagnetic Wave

A type of wave, such as visible light or infrared radiation, that can propagate through empty space and does not need a medium to travel.

Transverse Wave

A wave type, such as light, in which the wave motion or oscillation is perpendicular to the direction of energy propagation.

Opaque

A characteristic of an object or material that absorbs or blocks all incident light, preventing light from passing through and forming a shadow.

Translucent

A characteristic of a material that allows some light to pass through while scattering it, preventing objects behind it from being seen clearly.

Transparent

A characteristic of a material that allows light to pass completely through in straight paths, allowing objects behind it to be clearly visible.

Law of Reflection

A rule of optics stating that the angle of incidence is always equal to the angle of reflection ($i = r$), measured relative to the normal.

Normal

An imaginary reference line drawn at a right angle ($90^\circ$) to the reflective or boundary surface at the point of incidence.

Refraction

The bending of a wave (such as light) towards or away from the normal as it passes from one medium to another due to a change in wave speed and optical density.

Convex Mirror

A curved mirror with an outward-bowed reflective surface that causes incident parallel light rays to diverge.

Concave Mirror

A curved mirror with an inward-curving reflective surface that causes incident parallel light rays to converge.

Pupil

The opening in the centre of the eye that allows light to enter.

Iris

The coloured muscular structure of the eye that controls how much light enters by dilating in the dark or constricting in bright conditions.

Retina

The sensory surface located at the back of the eye onto which light is refracted and focused to form images.

Optic Nerve

The nerve pathway that carries electrical image signals from the retina to the brain.

Cornea

The clear, outermost curved front surface of the eye that protects the eye and assists in refracting incoming light.

Frequency

The number of wave cycles that pass a given point in one second, measured in Hertz ($\text{Hz}$).

Pitch

The musical characteristic of a sound indicating how high or low it is, determined by the frequency of the sound wave.

Amplitude

The maximum height of a wave from its rest position to a crest, which determines the volume or loudness of a sound wave.

Echo

A sound heard again after its wave reflects off a hard, distant boundary surface.