Thermal Energy Y9 Flashcards
What are the main processes in conduction?
1) neighbouring atoms transferring kinetic energy to each other through vibration
2) delocalised electrons collide with ion and transfer thermal energy to the ions
What is conduction?
Conduction is the transfer of thermal energy in solids.
Is trapped air a good insulator?
Yes. Anything with layers or pockets are good insulators because of this
What is convection?
Convection is the transfer of thermal energy in liquids and gases. This is achieved due to differences in density.
What is radiation?
The transfer of thermal energy via infrared waves. It can travel through a vacuum.
How does emitting and absorbing work?
Something emits when its warmer that it’s environment.
Something absorbs when its colder that it’s environment.
What are the steps of the convection current?
A) the air is warmed up and expands, so the density goes up and it rises.
B) after a while the air cools and compresses so it has a lower density and falls
C) as the air that used to be At c has risen, new cold air comes in to fill it’s place.
How do you work out payback time?
Cost of installation ÷ savings per year
How might you insulate using conduction?
Use a vacuum, as conduction needs matter, e.g. Vacuum flask
Use sir is it is a poor conductor of heat, e.g. Houses use fibreglass insulation to trap air
How might you insulate using convection?
Use a vacuum, as convection needs liquid or gas
Use trapped liquid/gas, as this restricts the circulation
How might you insulate using radiation?
Use shiny surfaces, as they are good reflectors of infrared, and poor radiators of heat
e.g. Space blankets for hikers
What are examples of conduction, convection and radiation?
Conduction: picking up a hot drink
Convection: inside of a greenhouse
Radiation: putting cold hands around a warm fire
What is payback time?
Measure of how cost effective a solution is
Payback time = cost of installation / savings per year
