Heat Transfer Flashcards
What is heat
A form of energy and transfers from hot places to cold places
Conduction
Only in solids
Metals = best conductors
Non-metals = best insulators
What makes a good insulator?
Best insulators are those which contains trapped air (eg wool), as it stops conduction
What happens in conduction
Heated atoms vibrate and collide with neighbours transferring the heat
In a metal free electrons can transfer heat quickly
Convention
Only in fluids (liquids or gases)
Atoms are free to move
Convention flow chart
Liquid heated - liquid expands - less dense - rises - cooler liquid falls to take place
Particles gain KE - move apart - rises - slower particles fall
Radiation
The way heat is transferred out of, or into a surface
What does the amount of radiation given off depend on
It’s temperature
It’s surface colour
The radiation is given off as …..
Infra red radiation
Experiment to test effect of surface colour on emission
1) place 2 cans (1 silver, 1 black) full of boiling water on to a polystyrene base with a polystyrene lid on top - add a thermometer
2) record temp every min for 20 mins
If an object is hotter than its surroundings it gives out what radiation
Heat
What objects are better emitters of radiation
Dark dull objects
What colour is the best emitter and absorber
Black
When heat energy is supplied to an object, its temp rises
The temp rise depends on:
1) heat supplied
2) mass of an object
3) the specific heat capacity of the material
Heat capacity equation
Heat supplied = mass x specific heat capacity x temp rise
