P1.1 Flashcards
All objects…
…emit and absorb infrared radiation
The hotter an object…
The more infrared radiation it radiates in a given time
Dark Matt surfaces =
Good absorbers and good emitters
Light stingy surfaces =
Poor absorbers and poor emitters but good reflectors
Solids…
…strong forces of attraction
Little energy
Vibrate in fixed position
Liquids…
…weaker forces of attraction
More energy
move about at random with low speeds
Gases…
…almost no forces
More energy
Move in random direction with high speeds
What does conduction happen in?
Solids
What does convection happen in?
Liquids and gases
What does radiation happen in?
Solids liquids and gases
Describe conduction
Vibrating particles pass on extra k.e to neighbouring particles
What are conductors?
Materials with particles very close together so conduct heat fastest
What are insualtors?
Materials which conduct heat more slowly because particles have spaces between them
Why are metals good conductors?
They have free electrons which collide with other free electrons and transfer energy
Is condition fastest in a short fat rod or a long thin rod?
faster conduction in a short fat rod
Describe convection
Air or water is heated
Expands and rises because it’s less dense
Particles with more k.e collide with colder particles and lose energy as they transfer it
Cooler water sinks because it’s more dense
Then it repeats
Describe condensation
Gas to liquid
As a gas cools it slows down and loses k.e so particles are pulled together to form a liquid
Water vapour condenses when it hits a cool mirror
How to increase the rate of condensation?
Lower gas temp
Lower temp of surface that gas hits
Higher density
Less airflow
Describe evaporation
Liquid to gas
Particles leave a liquid if they are traveling in the right direction and with enough energy/speed
Faster/hottest particles will leave first so temp of liquid will decrease and energy of remaing particles will decrease
How to increase the rate of evaporation?
Higher temp
Lower density
Larger s.a
More airflow
What factors increase the rate at which energy is transferred by heating?
Higher surface area and lower volume
The material the object is made - conductor or insulator
The surface the object is in contact with - conductor or insulator
How is a room heated by a radiator?
By convection currents and they have a large surface area
Why do cars have fins?
To increase the s.a so heat is radi rated quicker and the engine cooks
What are heat sinks?
Transfer heat away from objects they’re in contact with
They have fins and a large s.a to emit heat asap
Describe the vacuum flask
- Double walled with a vacuum between the walls - stopping conduction and convection
- Silvered walls to reduce heat loss by radiation
- Insulating foam minimising heat loss by conduction
- A stopper made of plastic and filled with cork or foam to reduce heat conduction
How do humans and animals control temperature when it’s cold?
Hairs stand up to trap a layer of insulating air limiting convection
Arctic animals have fur and smaller ears to minimise heat loss by radiation
How do humans and animals control temperature when it’s hot?
Blood flows to skins surface and is lost by radiation
Animals have larger ears in warmer climates to lose heat by radiation eg desert fox
How can energy be transferred?
By work or heating
How to reduce heat transfer in homes?
Cavity wall insulation stopping convection, conduction and radiation
Loft insulation stopping conduction and convection
Draft excluders reducing convection
Hot water jacket reducing conduction and convection
Thick curtains and carpets reducing conduction and convection
Foil behind radiators reducing conduction and radiation
Double glazing creating a vacuum and reducing conduction and convection
The bigger the temp differences between an object and its surrounding…
…the faster the rate at which energy is transferred by heating
What do u-values measure?
How effective a material is as an insulator
The lower the U-value…
…the better the material is as an insulator
How do solar panels work?
Contain water which is heated by radiation from the sun
Often painted black which is a good absorber
They can then heat building or be used as hot water
What does the specific heat capacity measure?
The amount of energy required to change the temperature of one kilogram of the substance by one degree
What is the specific heat capacity of water?
4200j/kg degrees c
Do the materials used in heaters have a high or low specific heat capacity?
High so they can store large amounts of energy
Why does water have a high specific heat capacity?
So it can be pumped around in pipes for central heating
How do electric storage heaters work?
Store heat using concrete or bricks at night and release it during the day
How do oil filled heaters?
Lower specific heat capacity than water meaning it’s not S good
But oil has a higher boiling point so can reach higher temperature
