Heat Transfer Flashcards
What are the 3 main methods of heat transfer?
Conduction, convection, radiation.
What is heat?
A form of energy.
When is heat energy transferred?
When there is a temperature difference.
How does conduction work?
The molecules in the hotter part vibrate more vigorously and transfer energy to their neighbours by collision.
Why does conduction mainly occur in solids?
The molecules are closely packed and can only vibrate about fixed positions.
What are the properties of insulators and conductors?
Insulators are bad conductors of heat
Conductors are good conductors of heat
What are fluids?
Liquids and gases (things that can flow)
Why can convection not occur in solids?
The particles can not move around
Why can convection not occur in a vacuum?
There are no particles
Describe a convection current.
The water is heated - molecules gain energy, get faster and spread out
The hot water becomes less dense
The hot water rises and floats on the cold water
The cold water is denser and sinks.
Evaporation and Condensation
Fuck it, look at page 69 of your physics book
4 factors increasing the rate of evaporation:
The surrounding air is hotter
The surface area is larger
There is a draught blowing water vapour away
Air humidity is low.
Why do all matters of state expand when heated?
The atoms vibrate more and take up more space; pushing each other apart.
An example of a use of thermal expansion.
In thermometers.
3 factors that increase the rate of heat transfer.
A larger surface area compared to volume
A larger temp. difference with the surroundings
Nature of the surface (see radiation).
