Transfer of Thermal Energy

Flashcards covering the mechanisms of conduction, convection, and radiation, thermal equilibrium, the greenhouse effect, and practical thermal applications based on IGCSE Physics notes.

Conduction

The main method of thermal energy transfer in solids, occurring when thermal energy is transferred from a hotter object to a cooler object in contact, or throughout a heated solid.

Atomic vibrations

A mechanism of conduction in all solids where atoms at the hotter end vibrate more, bumping into each other and transferring internal energy until thermal equilibrium is achieved.

Free electron collisions

An extended mechanism of conduction in metals, which are the best thermal conductors because they have a high number of free electrons.

Fluids

Liquids and gases that are poor conductors of heat; in liquids, particles slide past each other, while in gases, they are too widely spread to easily pass vibrations.

Best Insulators

Materials like rubber, glass, and air that are poor at conducting thermal energy compared to metals like copper and iron.

Convection

The main method of heat transfer through liquids and gases, occurring only in fluids when changes in temperature cause changes in density.

Convection current

The motion created when a heated fluid expands and becomes less dense, causing it to rise while cooler, denser fluid moves in to replace it.

Potassium permanganate demonstration

A simple experiment where crystals are placed in a beaker of water; when heated, they dissolve and rise with the warmed water to reveal the convection current.

Thermal radiation

The only method of heat transfer that can travel through a vacuum, consisting of infrared radiation from the electromagnetic spectrum.

Black objects

Surfaces that are very good at both absorbing and emitting thermal radiation, used in applications like laptop chargers and car radiators to help them cool down.

Shiny objects

Surfaces that reflect thermal radiation, absorbing very little and emitting very little, which causes them to take longer to cool down.

Leslie cube

A tool used to investigate thermal radiation by filling it with hot water and measuring the IR emission from its different surfaces: matte black, shiny black, white, and shiny silver.

Thermal equilibrium

A state reached when an object absorbs radiation at the same rate as it emits radiation, resulting in a constant temperature.

The Greenhouse Effect

A process where greenhouse gases in the atmosphere absorb and reflect back longer-wavelength infrared radiation emitted by the Earth, making the planet warmer.

Greenhouse gases

Atmospheric gases such as water vapour, methane, and carbon dioxide that trap heat by preventing longer-wavelength radiation from escaping into space.

Earth's night temperature (no atmosphere)

The temperature the Earth's surface would drop to without an atmosphere, estimated at approximately $-180\,^{\circ}C$, similar to the Moon.

Cooling Curves experiment

An investigation where the independent variable is the color of the flask and the dependent variable is temperature, showing that black flasks cool fastest and silver flasks cool slowest.

Solar Panels (insulation)

Components that reduce heat loss by using insulated material at the back and glass to trap air, which acts as a good insulator.

Thermos Flask (vacuum)

A feature of the flask that prevents heat loss by conduction and convection because there are no particles to transfer energy.

Thermos Flask (silver coating)

A feature designed to minimize heat loss through radiation by reflecting the radiant heat back into the liquid.

Car Radiator (metal fins)

Components with a large surface area that are colored black to increase the rate of thermal energy radiation and cooling.