3 - Heat Flashcards
Which colour emits and absorbs heat best?
(Matte) Black
Which colour emits and absorbs heat worst?
Silver (Foil)
Which of these transfers energy better?:
a) a sourcepan on a hob with boiling water
b) boiling water inside a sealed flask
A - The heat energy is transferred out of the saucepan and into the air
The thermos flask is a closed system as no energy can escape
What types of energy transfers are used when heating objects?
Heating - energy transferred from hotter to colder objectsRadiation - energy transferred by waves (eg sun rays -> earth)
What do particles do when an object is heated?
The particles in the hotter part vibrate more & collide with each other, transferring heat energy to other particles
What is conduction?
The transfer of energy from an object’s stores to another object’s energy stores, making their particles vibrate faster
What is thermal conductivity?
How well an object transfers energy by conduction
What materials have a high thermal conductivity?
Metals - Heat transfers through the particles in a metal quickly
What materials have a low thermal conductivity?
Gases (eg air)
Why do houses need walls with a low thermal conductivity?
As it’s good to have a slow rate of energy transfers through them
What else keeps houses warm?
Thick walls - the thicker the wall, the slower the rate of energy transfer
What else stops a house losing heat energy?
Using thermal insulators (objects made from materials that don’t transfer heat well)
How do double glazing or cavity walls in a house work?
There is an inside wall and an outside wall and an air gap in between
The air gap is not a good conductor of energy so this reduces the amount of energy transferred by conduction through the walls
Why is fibre glass wool used in the loft or around water tanks?
It’s thick so reduces the rate of energy transfer through the ceiling into the loft space
What is convection?
The transfer of heat through liquids
