4b - energy transfers
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16 Terms
state the eight energy stores.
kinetic, elastic, magnetic, electrostatic, nuclear, gravitational, thermal, chemical
state the four energy transfers.
mechanically, electrically, by heating, by radiation
state the principle of the conservation of energy.
energy can only be transferred, never created nor destroyed
what is the relationship between efficiency, useful energy output and total energy output?
efficiency = (useful energy output / total energy output) x 100%
what is efficiency measured in?
joules (J)
what is conduction?
the transfer of thermal energy through collisions of touching particles
how does conduction work?
particles closest to the thermal energy sources gain more kinetic energy and vibrate with greater amplitude
this causes them to collide with neighbouring particles and pass on some kinetic energy
the process continues
why are metals particularly good conductors?
because they have a sea of delocalised electrons which can easily move through the metal to transfer thermal energy to all atoms
what is meant by the term 'thermal conductor'?
a material that transfers thermal energy fastest by conduction
what is meant by the term 'thermal insulator'?
a material that transfers thermal energy slowest by conduction
what is convection?
thermal energy transfer in fluids
how does convection work?
molecules closest to the thermal energy source gain kinetic energy
they move faster and spread out
as a result the hot air expands
its density decreases
the hot air rises above the cold air
the cold air moves into place
the cycle repeats until temperature is even
known as a convection current
what is radiation?
thermal energy transfer in empty space via infrared waves
what surface is the best emitter and absorber of radiation?
matte and black surfaces
what surface is the worst emitter and absorber of radiation?
shiny and white
how does a vacuum flask reduce heat loss?
the vacuum contains no particles, and therefore stops conduction or convection from taking place