CHP 9 transfer of thermal energy Flashcards
What is thermal equilibrium?
When there is no more net transfer of thermal energy between eg. 2 objects
What is conduction?
Conduction is the transfer of thermal energy through a medium due to difference in temperature without the movement of the medium itself
How does conduction occur in a rod through molecular vibration?
When one end of the rod is heated, the particles at that end gains thermal energy and starts vibrating vigorously about its fixed position, colliding with neighbouring particles, which were vibrating at a slower rate. The faster moving molecules than transfer some kinetic energy to the slower moving ones, causing them to gain kinetic energy and start to vibrate faster too, colliding with the next layer of slower molecules. Thermal energy is then transferred from on particle to the next and in the end, the particles at the other end will also start vibrating fast and the cooler end becomes hot.
How does conduction occur in a metal rod through free electron diffusion?
When one end of the rod is heated, the free moving electrons move faster by gaining kinetic energy, drifting towards to cooler parts of the rod and imparting their kinetic energy to the particles they collide with, causing those particles to also gain kinetic energy and vibrate faster too.
What is convection?
Convection is the transfer of thermal energy by convection current in a fluid due to the difference in density.
Which states can conduction occur in?
Liquid and gaseous (fluid)
Which states can conduction occur in?
Solid, liquid and gases
How does convection occur in liquids (water) if a candle is placed below the beaker? if qn is about gas, just change the liquid to gas
As water is heated from the bottom, it gains thermal energy and expands, causing its density to decrease and hence rising to the top of the beaker. Cooler water at the top are denser than the heated water and will sink to the bottom of the beaker to replace the heated water. It then gets heated and rises. This cycle is repeated to form a convection current that transfers heat throughout the liquid until it reaches thermal equilibrium.
Why does convection not occur in solids?
because it is a method of heat transfer involving the movement of particles in the medium, hence cannot happen in solids.
What is radiation?
Radiation is the transfer of thermal energy by infra-red radiation, without the need of a medium.
What is an emitter/radiator of radiation?
any substance that gives off heat by radiation
Which surfaces are good absorbers and radiators of heat?
Black surface, dull, rough surfaces
Which surfaces are poor absorbers and radiators of heat?
White surfaces, shiny, smooth surfaces
