Energy transfer Flashcards
Where is thermal energy transferred from
a place that is hotter or a high tempreture to an area with a lower tempreture or cooler
What are the 3 processes of energy transfer
Conduction, Convection and radiation
What is Conduction
The transfer of thermal energy through a substance by the vibrations of atoms within a substance
Explain conduction
The process of conduction happens by the vibrations between the atoms of a substances these vibrations transfer kinetic energy from particles to other particles which is then transferred into thermal energy there will be more energy gained from this
What is convection
Convection is the transfer of heat through fluids by the upwards movement of warmer less dense regions of fluid and the downwards movement of more dense cooler particles.
Explain Convection
In convection the heated liquid will expand and become less dense then the cooler surrounding water. The warmer liquid rises to the top of the area and the cooler dense liquid sinks and takes its place At the top the warm liquid starts to cool and become more dense. It will begin to sink the cooler water then heats and rises so a circulation current is set in the water this is the convection current.
Give an example of convection occurring in everyday phenomena
In many cooking ovens the heating element is placed at the bottom of the oven it heats the air nearest to it, and the air rises due to convection. The top of the oven is generally warmer than the bottom is. Air and water also allow heat transfer to take place by convection as both are fluids and good insulators
What is thermal radiation
The transfer of energy by infrared waves
What effects how much an object radiates
the hotter the object the more it radiates, the colour Black objects are the best at emitting and absorbing heat shiny object are the worst at emitting and absorbing thermal radiation
Explain which colours are the best and worst at absorbing and emitting radiation
-black good absorber good emitter
-dull/dark reasonable absorber/reasonable emitter
-white poor absorber poor emitter
-shiny very poor absorber very poor emitter
Explain how the 3 energy transfers occur in a in a hot cup of coffee
-Energy is transferred by heating from the bottom of the mug to the surface its in contact with energy transfer will happen through conduction
-Energy is transferred by radiation to the surrondings
-As heat rises due to convection most of the hot liquid is at the surface of the coffee so stream will rise away from the coffee due to the process of convection
Why will the coffee continue to lose heat
Hot liquids will tend to lose heat until they reach a thermal equilibrium
Why are metals good conductors
Metals are good conductors as their delocalised electrons can collide with the atoms helping to transfer the vibrations through materials and hence transfer heat better. Delocalised electrons in metals speed up thermal conductions
Why are noon-metals poor conductors or insulators
Non-Metals are poor conductors or insulators because they have very few free electrons to transfer vibrations through materials so they cannot transfer heat well. The same with gases and liquids they do not have any free electrons so they cannot pass on the current
Explain how emission and absorption of radiation is related to surface area
If surface area is a good reflector of infrared radiation then it is a poor emitter of IR. This means that a hot object with a shiny surface will emit less heat energy in the form of infrared radiation than other object of the same tempreture with a matt black surface. A kettle with a shiny surface is shiny to reduce the rate of heat loss
