Energy Transfers Flashcards
How many ways can thermal energy be transferred?
3
What determines the effectiveness of heating mechanisms?
The state of matter
What are the three heating mechanisms?
- Conduction: mainly in solids
- Convection: only in liquid and gases (can flow)
- Radiation: heating by IR radiation waves, in all objects
What makes a good conductor?
In good conductors, particles are close together, hence they are more dense, as this allows collisions between particles to occur more rapidly. Solids are good conductors and gases are very bad. They must have many delocalised electrons, that collide with different nuclei, transferring energy from one place to another, when materials are touching. This evenly distributes energy, to level the temperature difference.
Conduction in non-metals
When you heat one end of an object, particles start vibrating more. These particles collide with their neighbouring particles. Thermal energy is transferred through the solid by these collisions between the particles. This is known as conduction.
Conduction in metals
When a metal bar is heated at one end, the free delocalised electrons at that end diffuse faster through the metal. They collide with other free electrons. As a result, they transfer energy from the hot end of the metal, levelling the temperature difference. The free electrons also collide with the atoms and make them vibrate more.
Is the fluid the same as a liquid?
NO! Fluids include gases as well as liquids.
What floats, less dense or more dense?
Less dense floats on more dense
Convection current description
At the heat source, the liquid is heated, the particles gaining energy, and overcoming the attractive force between them, spacing out, and causing the liquid to expand. This results in it being less dense. The hot liquid then rises due to the lower density. Further away from the heat source, the liquid loses energy, cooling and contracting, the density increasing, as energetic particles are lost through evaporation. Finally, the cooled liquid sinks and falls due to increased density.
What is radiation?
Radiation is heating by IR radiation waves, in all objects.
What is infrared radiation?
Infrared radiation is similar to light, in the form of electromagnetic waves, that transfer thermal energy. It is able to travel through a vacuum, not requiring a medium (like sound waves), giving us heat from the Sun. It is emitted by all objects, varying based on the heat on the object.
Black surfaces and IR radiation
If a surface is a good absorber of IR radiation, it is also a good emitter of IR radiation. Black surfaces are the best emitters or absorber of IR radiation.
Shiny surfaces and IR radiation
Shiny surfaces are best at reflecting IR radiation
