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thermal energy can be transferred from all objects by ....... even thorugh empty space (...)
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thermal radiation can be used in
- infrared heaters
- passive infra red devices (PIRs)
- thermal imaging cameras
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an infrared heater is a body with a :
high temperature which transfers energy a body with a lower temperature through electromagnetic radiation
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why do we get warm from an infrared heater
because our skin and clothes absorb the infrared
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why do we feel warm in the sun
because the infrared radiation that hits your clothes and skin keeps you warm
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there are several kinds of infrared heaters . some direct thier light straight into a room or space to create heat on the object it reaches . infrared heaters also differ in fuel sources and construction material . there are propane .... .... and .... heaters .some are ceramic , and there are also portable ones
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a passive infrared sensor (PIR sensor) is an electronic device that :
measures infrafed (IR) light emmited from objects in its field of view
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PIR sensors are often used in ..... .... . Motion is detected when and infraed source with one temperature , such as a human , passes in front of an infraed source with another temperature such as a wall .
motion detectors
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we had a radiant heater placed directly in gthe middle of two surfaces , one was a black surface and the other was a shiny surface . we held a coin to each surface with grease .
the coin fell off the .... surface first showing that the ..... surface was a better absorber of heat than a .... surface
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dark matt surfaces are good .... (poor ....) of radiation
light , shiny surfaces are good ..... (poor ....) of radiation
- absorbers
- reflectors
- reflectors
- absorbers
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thermal (infrared) radiation is :
the transfer of electromagnetic (infrared) waves , particles of matter are not invloved in thermal radiation
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all obejects ...... and .... radiation
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the .... an object the more energy it radiates in a given time
warmer
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... ... surfaces are good absorbers and good emiters of radiation
matt black
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..... ... surfaces are poor absorbers and poor emiters of radiation
shiny bright
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.... ..... are good reflectors of radiation
shiny bright
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in a solid , a liquid and a gas what is the arragnement of particles
- solid - close together and in aregular pattern
- liquid - close together but random
- gas - far apart and random
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label the diagram
- A = sublimation
- B = melting
- C = freezing
- D = evapourating or boiling
- E = condesing
- (do not need to no A)
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what main factor affects the rate of evapouration and condensation
temperature
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define conduction
the transfer of energy by a substance , without the substance moving itself is called conduction
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list the following metals in order of thier effectivness of conducting : aluminium , copper , brass , iron
- copper
- aluminium
- brass
- iron
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metals are very .... conductors and .... insulators . non metals are usually ..... conductors and gases are .... conductors
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why are metals good conductors of heat
because they contain lots of elctrons that can move about freely
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when a metal bar is heated at one end , the elctrons at that end .... ... . They .... with other free electons . As a result they .... energy from the hot end of a metal . the free electrons also .... with the atoms and make them .... more
- move faster
- collide
- transfer
- collide
- vibrate
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define convection
liquids and gases can flow and so can carry energyf rom places where the temperatrue is higher to places where the temperature is lower . transfer of energy by liquids or gases moving in this way is called convection
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convection currents occur in ... and ... because thier particles move ... .... when they are hot causing the liquid or gas to .... . when particles move apart they make a fluid less ... . warm regions are then less ... than cold regions . the warm fluids .... through the colder ones and colder fluids replace the warmer ones which have risen
- liquids
- gases
- more freely
- expand
- dense
- dense
- rise
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