Transfer of thermal energy Flashcards
How is heat transferred in solids (conduction)?
the particles which vibrate about a fixed spot gain energy, colliding with the particles next to them and transferring thermal energy
Define ‘conduction’
heat transfer from a hotter to a colder place through a material either by:
- vibration of its atoms
- free electrons (for metals)
Why are metals good thermal and electric conductors?
their delocalised electrons can move throughout the metal
How does conduction occur via delocalised electrons?
electrons gain ke from hot end of metal, moving and colliding with atoms, increasing their KE and temp.
Why are gases poor thermal conductors?
the particles are far apart, making it hard for energy to be transferred from one particle to another
Why are most liquids poor thermal conductors?
since particles are free to flow, making it hard for energy to be transferred easily as it is a lattice
What is one experiment to test conductivity?
put boiling water in a box with holes
place rods of different materials in these holes
place drawing pins held with petroleum jelly on the far ends of rods
see which drawing pins fall of first due to conduction of heat from water
Define ‘convection’
method of thermal energy transfer in liquids and gases
How does convection work in liquids/gases? What is the name given to this movement?
hot fluid expands, becomes less dense and rises
cold fluid sinks as it is more dense
the colder fluid is then heated and rises again, forming a convection current
What is a convection current?
movement of fluid that transfers heat energy upwards
Describe one experiment to test convection
fill a beaker with water, then place a potassium manganate crystal into the beaker
place a bunsen burned flame right under the crystal
you will see the convection from the movement of color in the beaker
Define ‘radiation’
heat transfer from a hot to a colder place by infrared electromagnetic waves
Which object emit thermal/infrared radiation?
all of them :)
Does infrared radiation require a medium?
no, like all electromagnetic waves
Which colours and textures are good emitters and absorbers of heat energy?
dark colours (black)
dull textures
