chapter 10 Flashcards
SI unit for temperature
K, kelvin
heat is transferred from…
a hotter region to a cooler region
heat results in…
- expansion
- contraction
expansion in liquids (rising sea levels)
- due to climate change and global warming, the oceans absorb more heat energy
- expand and sea levels will rise
- coastal erosion
expansion and contraction in gases (metal pipes)
- metal pipes carrying steam are very flexible
- can expand and contract safely without breaking
opening a jar
- place cap of jar in hot water
- metal lid expand more than glass jar
- less tight and easier to unscrew
bimetallic strip
a strip made of 2 metals that expand at different rates
bimetallic strip example
- brass (expand more)
- steel (expand less)
bimetallic application
- thermostats
- bimetallic thermometers
thermomstats
help keep temperature of appliance constant
bimetallic strip in electric iron
- turn the knob sets the temperature of iron at which is switches off
- bimetallic strip in iron is strait and contacts are touching, forming a closed cicuit and allow electricity to flow through it
- bimetallic strip expands when heated. brass expand more than steel, causing the strip to bend downwards, causing an open ciruit
- this switches of the circuit
- when the strip cools down, it becomes straight and the contacts touch again
bimetallic strip in thermometer
- bimetallic strip is made into a coil, attached to a pointer
- as temperature changes , the different expansion rates of the metals cause the coil to unwind (temp increase) or tighten (temp decrease)
hot air balloon
- when air in hot air balloon is heated, the volume increase, while the mass stays the same
- causes density to decrease, and the air to to rise
- balloon floats
how can heat be transferred
- conduction
- convection
- radiation
conduction definition
transfer of heat without the physical movement of the medium
states of matter conduction rates
- solid
- liquid
- gas
why is solid better conductor of heat
- the particles are arranged closely to each other in an orderly matter.
- when the particles gain energy, the transfer of the energy is more quick
convection definition
the transfer of heat with the physical movement of the medium
convection can be used for:
fluids (liquid and gas)
convection in liquids
- as the water at the bottom gain heat and expands, the density decreases, causing it to rise to the top, as seen with the purple colouring
- cooler and denser water sinks to the bottom as it is more dense than the surrounding water at the top, as seen with purple colouring going downwards
- hotter and less dense water rises, and cooler and more dense water sinks, forming a convection current.
- after a while, the heat is evenly distributed, and the colour of the water is purple
convection in gases
- air above candle gains heat, expands, become less dense, and rises chimney A
- cooler air plus smoke from paper move down chimney B into the container as it is less dense.
- takes up space of the hotter air
- gains heat and rises, forming a convection current
radiation
transfer of heat from a hotter body to a cooler body without the need for a medium
- can take place in vaccum
greenhouse effect
warming of the surface of earth
- heat is prevented from leaving earth by radiaiton
- greenhouse gases trap the heat
factors affecting radiation
- temperature of object
- surface area of object
- colour of object
- texture of object
factors affecting conduction
- different materials
temperature of object
- hotter the body, the higher rate of radiation from the object
surface area of object
- higher the surface area, the higher the rate of radiation
heat sink radiation
- large surface area -> allows heat to be radiated from the appliance quickly
absorption of radiation
- dull, rough surfaces are better absorbers of heat the radiation
emision of radiation
- dull, rough surfaces are better emitters of radiation
reflection of radiation
- light/silver coloured surfaces can reflect radiation well
- petrol: prevent them from heating up
air condition convection
cold air released from the aircon is denser than the surrounding air, and will sink.
heater convection
cool air near the heater gains heat, expands, becomes less dense and rises, causing cool air to replace the replacew the space taken up by the air previously
sea breeze
- clockwise
- sun heats up land, which warms air above it, becoming less dense and rises.
- air above the cooler sea replaces the air above the land
land breeze
- anti-clockwise
- layer of air above sea is warmer, becoming less dense and rises
- air above the cooler land moves to replace the air above the sea
building and clothes radiation
- things are painted white because they are poor absorbers of radiation from the sun
clothing fins radiation
- dull black to emit heat to surroundings
kettles and pots radiation
- silver and polished which is a poor emitor of heat, keeping contents warm
emergency blanket
- shiny surface: poor emitter of heat, will not emit heat form the body to surroundings
solar collector
- painted black to absorb most amount of radiation
- heat running inside transferred from tubes to water by conduction
vacuum flask (hot)
- reduce heat loss by conduction
-> insulated cap reduces rate of heat loss by conduction - reduce rate of heat loss by convection
-> keeping cap screwed tightly prevents heat loss by convection - reduce rate of heat loss by conduction
-> insulated support reduces rate of heat loss by conduction - prevent heat loss by conduction
-> vacuum between walls prevent heat loss by conduction as it cannot occur in a vacuum - reduce rate of heat loss by radiation
-> silvere lined walls reflect heat and reduce rate of heat loss by radiation
THATS IT YAYAYAYA
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