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- Created by: elisha.ks
- Created on: 06-03-17 22:22
what is infrared radiation
emission of electromagnetic waves
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what do all objects do
emit and absorb infrared radiation
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the hotter an object is...
the more infrared radiation it radiates in a given time
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dark, matt surfaces =
good absorbers and emitters of IR radiation
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light, shiny surfaces =
poor absorbers and emitters of IR radiation but good reflectors
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kinetic theory for solids
strong force of attraction holds particles close in fixed, regular arrangement, low energy so vibrate around fixed position
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kinetic theory for liquids
weaker forces of attraction so close but can move and form irregular arrangement, more energy move in random directions at low speed
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kinetic theory for gases
almost no forces of attraction, most energy free to move, random directions at high sppeds
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what does heating a substance do
give particles more KE, vibrate or move faster causing solids to melt and liquids to boil
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conduction
solids, vibrating particles pass extra KE to neighbours, rise in temp at over side as heat passes through
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when is conduction faster
in dense solids: particles closer together, collide more often + pass energy
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what are insulators
materials w large spaces between particles so conduct heat energy slow
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why are metals good conductors
free moving electrons
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convection
liquids+gases, more energetic particles move from hotter to cooler region
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what causes convection currents and what do they do
changes in density, circulates heat energy
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condensation
gas to liquid, when gas cools particles slow down and lose KE, attractive forces pull particles closer together
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evaporation
particles escape from liquid, when temp is much lower than the liquids boiling point
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particles near the surface of liquid can escape and become gas particles if...
travelling in right direction, have enough KE + speed to overcome attractive forces
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explain cooling effect
fastest particles most likely to evaporate, so avrg speed+KE of remaining particles decreases, temp of liquid falls, liquid cools
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rate of evaporation is faster if
larger surface area (more particles near surface), higher temp (more KE), airflow over liquid greater(conc of gas in air lower), density lower(weaker forces to overcome)
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rate of condensation is faster if
higher density(stronger forces), less airflow(conc of substance in air higher), temp of surface the gas touches is lower, temp of gas is lower
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rate at which object transfers energy by heating depends on...
surface area and vol, material of object, nature of surface with which object is in contact
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cooling fin adaptions
increased surface area, heat radiated away quicker, engine cools quicker, black to emit heat quicker
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bigger the temp difference between object and its surroundings..
the faster the rate of energy transfer by heating
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purpose of a vacuum flask
reduce/limit heat transfer
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5 features of vacuum flask and why
double walled with vacuum between, silvered walls, insulating foam, plastic stopper filled with cork
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How do humans control heat transfer in the cold
hairs on skin stand up, trap layer of insulating air, limits heat loss by convection
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how do humans control heat transfer in the warm
body diverts more blood flow near surface of skin so more heat can be lost via radiation
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how do animals control heat transfer in cold
small ears/surface area = minimise heat loss by radiation and conserve body heat
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how do animals control heat transfer in warm
large ears/surface area = lose heat by radiation easily and keep cool
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what are the most 'cost-effective' methods
those that give the biggest anual saving
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payback time =
initial cost / annual saving
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what is cavity wall insulation
foam squirted in brick gaps to stop convection currents in gap, radiation across gap, air pockets trapped help reduce heat loss by conduction
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what is loft insulation
thick layer of fibreglass wool laid across floor to reduce heat loss by conduction and convection
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what are u values
measure how effective a material is as an insulator
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the lower the u value...
the better the material is as an insulator
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how do solar panels work
water pipes under black surface so radiation from sun absorbed and heats water - used to heat buildings or provide domestic hot water
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what is specific heat capacity
how much energy a substance can store/ amount of energy required to change 1kg of a substance's temp by 1c
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what is water's shc
4200J
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water in heaters
high shc, liquid, easily pumped around pipes, ideal for central heating in buildings
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concrete/bricks in heaters
electric storage heaters store heat energy at night (electricity cheaper) then release in day, high shc
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oil in heaters
lower than water's shc, often not as good, has higher boiling point than water so heaters can safely reach higher temps than water ones
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Other cards in this set
Card 2
Front
what do all objects do
Back
emit and absorb infrared radiation
Card 3
Front
the hotter an object is...
Back
Card 4
Front
dark, matt surfaces =
Back
Card 5
Front
light, shiny surfaces =
Back
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