Thermal energy always flows from a region of higher temperature to a region of lower temperature.
8.2 Conduction
Conduction is the process of thermal energy transfer without the medium flowing.
Occurs mostly in solids, good conductor of heat.
Thermal energy is supplied to a material -> Particles at hot end vibrate vigorously -> Particles collide with neighbouring particles -> Kinetic energy is transferred to the neighbouring particles.
This happens because metals contain many free electrons which move randomly between the atoms or molecules.
8.3 Convection
Convection is the transfer of thermal energy by means of currents in a fluid or gases.
When water at the bottom of a container is heated, it expands -> Expanded water is less dense and start to ride -> Cooler regions of the water in the upper part on container became denser and sinks.
Convection currents occur only in fluids such as liquids and gas but not in solids.
Because convection involves the bulk movement of the fluids which carry thermal energy with them.
8.4 Radiation
Radiation is the continual emission of infrared waves from the surface of all bodies, transmitted without the aid of a medium.
The process in which energy is emitted as particles or waves.
Radiation can take place in a vacuum.
Factors affecting rate if infrared radiation
- Colour and texture of the surface
- Surface temperature
- Surface area
Emission = give out
Best absorption and emission: dull black surface
No comments:
Post a Comment