energy Flashcards
what are the golden rules for energy?
Energy cannot be created or destroyed
it can only be transferred from one store
to another store.
ENERGY IS MEASURED IN JOULES (J)
ENERGY IS MOVED FROM ONE ENERGY
STORE TO ANOTHER (‘TRANSFER’) by
MECHANICAL WORK, ELECTRICAL WORK,
HEATING, OR RADIATION
what does energy allow?
ENERGY ALLOWS WORK, RADIATION AND HEATING TO BE DONE.
how is energy transferred mechanically?
when a force moves something through a distance.
how is energy transferred by heating? (H)
when a temperature difference causes a transfer of energy from one place to another by conduction or convection.
how is energy transferred electrically?
when an electric charge moves through a potential difference; this is the main method of energy transfer in electric circuits.
how is energy transferred by radiation? (R)
carried by waves in the electromagnetic spectrum (this includes Radio, microwaves, infra-red, visible light, ultra-violet, x-rays and gamma), or by mechanical waves such as sound.
what is conduction?
how thermal energy flows through a substance without moving.
what is convection?
transfer of heat through fluids by the upwards movement of warmer, less dense regions of fluids.
how does heat move?
heat moves from somewhere hot to somewhere cold.
what are the best conductors of heat?
solids and metals
what are the worst conductors of heat?
gasses
what is a poor conductor called?
an insulator
does a vacuum allow conduction or convection?
no
how does thermal conduction occur by molecules?
the molecules vibrate when heated, intermolecular forces allow the molecules to pass their vibrations from one to another. the stronger the forces the faster vibrations are passed.
how does conduction occur through metal?
they have electrons that can move from one atom to another. these electrons can pass energy through the metal very quickly.
why is diamond a good conductor?
because it has strong intermolecular bonds
how do you speed up the rate of thermal transfer?
by using a better conductor
by decreasing the thickness of the substance
by increasing the are of the substance
by increasing the temp difference across the substance
what is thermal radiation?
the transfer of energy by infrared waves
which surfaces emit radiation the best
dark, rough surfaces.
which surfaces absorb radiation the best
dark, rough surfaces
which surfaces reflect radiation the best
bright, polished surfaces
name a method of heat transfer in solids. Describe, in terms of particles, how energy is transferred through the solid block by this method.
conduction because the molecules vibrate when heated, intermolecular forces allow the molecules to pass their vibrations from one to another.
where can convection not take place and why?
in solids because convection travels fluids not solids as the particles in a solid are tightly bonded and you need them to flow for convection.
when humans are cold the hairs on their bodies stand on end. explain how this reduces heat loss in the body.
when the hairs stand up they trap a layer of air and air is a good insulator.
suggest one way in which heat loss can be reduced from the human body.
wearing clothes because when you wear clothes they trap a layer of air is a good insulator.
A homeowner is considering having a cavity wall insulator installed. state one transfer this will help reduce.
conduction because cavity insulated walls stop the hot air from rising.
how is heat loss reduced in doors, windows, roofs, floors and walls?
doors - draught excluders windows - double glazing/curtains roof - lost insulation floors - carpets walls - cavity wall insulators
how can you reduce heat loss in a flask?
conduction - reduced by the vacuum, stopper, glass, cork and air spaces
convection - reduced by the vacuum, stopper and the trapped air spaces
radiation - reduced by the silvered walls.
