Transfer of Thermal Energy

Comprehensive vocabulary flashcards detailing the mechanisms of conduction, convection, radiation, and the greenhouse effect, alongside corresponding experimental demonstrations from the Cambridge IGCSE Physics curriculum.

Good thermal conductors

Solids that easily transfer heat, such as aluminium pans or copper wire.

Bad thermal conductors (Insulators)

Solids that do not transfer heat well and help retain thermal energy, such as a wool blanket, wood, or layers of cardboard or paper.

Tile versus rug conduction effect

A phenomenon where tiles feel colder than a rug at the same temperature because tiles conduct heat away from the foot rapidly, whereas an insulating rug does not transfer heat away.

Wood and metal cylinder experiment

A demonstration where paper wrapped around a joined wood and metal rod is heated; paper touching the metal remains undamaged because metal conducts heat away, while paper touching the wood chars because wood is a poor conductor.

Conduction ring apparatus

An experimental apparatus consisting of strips of different metals (such as iron, copper, brass, and aluminium) arranged around an insulated circle holding ball bearings with wax to determine their relative rates of thermal conduction.

Thermal conduction

The main method of thermal energy transfer in solids, occurring through atomic vibrations and the collisions of free electrons transferring heat from a hotter region to a cooler region.

Atomic vibrations (in conduction)

The mechanism occurring in all solids where heated atoms or ions vibrate more, bumping into neighboring particles and transferring internal energy until thermal equilibrium is achieved.

Free electrons (in metals)

Delocalised electrons present in high numbers in metals that move freely throughout the structure, rapidly transferring thermal energy via collisions.

Convection

The primary method of thermal energy transfer in fluids (liquids and gases), driven by changes in temperature causing changes in density; it cannot occur in solids.

Convection current

The circulating motion set up when heated fluid expands, decreases in density, and rises, while cooler, denser surrounding fluid sinks to replace it.

Potassium permanganate convection experiment

A practical demonstration in liquids where dissolving purple crystals reveal convection currents by rising with heated, expanding water and sinking as the water cools and becomes denser.

Thermal radiation

Infrared radiation emitted by the surface of all objects as part of the electromagnetic spectrum; it requires no medium and is the only method by which heat travels through a vacuum.

Black surfaces (thermal properties)

Surfaces that act as both good absorbers and good emitters of thermal (infrared) radiation.

Dull / dark surfaces (thermal properties)

Surfaces that act as reasonable absorbers and reasonable emitters of thermal radiation.

White surfaces (thermal properties)

Surfaces that act as poor absorbers and poor emitters of thermal radiation.

Shiny surfaces (thermal properties)

Surfaces that reflect infrared radiation, making them very poor absorbers and very poor emitters of thermal radiation.

Thermal equilibrium (radiation)

The state where an object absorbs thermal radiation at the exact same rate as it emits thermal radiation, maintaining a constant temperature.

Greenhouse gases

Gases in the Earth's atmosphere—including water vapour, methane, and carbon dioxide—that absorb and re-emit longer-wavelength infrared radiation back toward the Earth's surface.

Greenhouse effect

The process by which greenhouse gases trap longer-wavelength thermal radiation emitted by the Earth, keeping the planet warmer than the -18\,^\r\n\circ\text{C} it would be without an atmosphere.

Cooling curves of surface colours

A graph comparing heat loss over time among identical flasks painted different colours, showing that black cools at the highest rate while silver cools at the slowest rate.

Double-glazed window

A window featuring a trapped layer of air between two panes of glass, which acts as an insulator to reduce thermal energy loss by conduction.

Multiple paths of energy transfer (hot beverage)

The simultaneous transfer of thermal energy from a hot cup to the surroundings via conduction (through contact), convection (from the liquid surface to air), and radiation (from cup sides).

Car radiator

A cooling device that takes heat from an engine via a circulating liquid by conduction and emits it into the surrounding air mainly through radiation, enhanced by a dark colour and a large surface area.