PHY - Thermal energy

what are the 3 ways in which thermal energy can transfer and what is each for

convection - fluids

conduction - solids

radiation ( can occur in vacuum )

what does T_s stand for on a graph

Temperature surroundings

what is thermal equilibrium

when the surroundings and the object are the same temp.

temperature

a measure of the kinetic energy of the particles in a substance

how does a thermometer work

• particles in the substance collide with the particles of the thermometer giving them KE

• this continues until thermal equilibrium

• the liquid in the thermometer either expands or contracts as temp. changes

• the height is then read off the scales as temp.

what is absolute zero

the temp of the particles no longer contain any KE, they are completely still

273^oC

conduction

The transfer of thermal energy through solids from a region of high temp to a region of lower temp through the vibrations and movement of electrons

why is conduction important in solids not fluids

solids are in a fixed position so vibrations are passed on quickly

convection

the transfer of thermal energy through fluids by the bulk movement of the fluid itself

convection currents

• close to the heat source, the hot fluid expands cause particles to become further apart

• this cause the hot fluid to become less dense

• meaning the hot fluid will rise and be replaced by colder fluid

• far from the heat source, cooler fluid contracts and becomes more dense therefore sinking

why is sea breeze common during hot days and land breeze common at night

at night the sea remains warmer than the land so the air above the sea is warmed and rises as it becomes less dense, this causes the cool air above land to be sucked to the sea to replace it causing a breeze.

converse

radiation

the transfer of thermal energy by electromagnetic waves

the hotter the object…

the more thermal radiation emitted

best emitter of thermal radiation

black and matte surface - therefore will cool fastest

worst emitters of thermal radiation

white and shiny surfaces

best colour to wrap food in

white = poor at absorbing thermal energy, will reflect it back into the potato

worst colour of clothes on a hot sunny day

black since its a good absorber you will get hotter

why are radiators usually painted white why not black

they could become too hot and cause burns

how does sweating help us cool down

the particles that escape and become gas have a greater kinetic energy this means the overall kinetic of the fluid decreases so it cools down

how does a thermos/ vacuum flask reduce transfer of energy by conduction

vacuum and double walled glass

how does a thermos/ vacuum flask reduce transfer of energy by convection

stopper and vacuum

how does a thermos/ vacuum flask reduce transfer of energy by radiation

silver wall to reduce absorption