Understanding Heat Transfer Flashcards
State the three rules of heat transfer .
-Heat always moves form a warmer place to a cooler place.
-Hot objects in a cooler room will cool to room temperature
-Cold objects in a warmer room will heat to room temperature
State the three heat transfer methods
-Conduction
-Convection
-Radiation
Describe Conduction in metals
-The delocalized outer electrons of a metal drift and are free to move.
-When the metal is heated, this ‘sea of electrons’ gain kinetic energy
-The kinetic energy causes the particles in a metal to vibrate
-These vibrations make the adjacent particles to vibrate
-Vibrations are passed along the metal and so is the heat.
What are insulators ?
-Insulators are usually non-metals and they do not conduct heat
-They do not conduct heat because they don’t have this ‘sea of electrons’
What feature of metal allows them to conduct heat?
-They have a sea of delocalized electrons that drift and are free to move in the outer space of electrons
Why do metals feel colder than wood when you touch them, if both are at the same temperature?
-Metal is a conductor, wood is an insulator. Metal conducts the heat away from your hands. Wood does not conduct the heat away form your hands . So the the wood feels warmer than the metal.
Convection works on what states of matter?
Liquid and gas
Conduction works on what state of matter?
Solids
Describe convection current
1) Particles of gas or liquid are heated
2) They gain thermal energy and kinetic energy
3)Because of the kinetic energy they start to vibrate more
4)Because of the vibration they start to occupy more space, and become less dense
5)Less dense particles are lighter particles so they rise .
6) Cooler air has less thermal and kinetic energy
7)So particles vibrate less and occupy less space and are closer together, which makes them more dense
8) More dense particles tend to be heavier
9) less dense particles rise and more dense particles sink to replace the space of the less dense particles .
10)This cycle repeats
What happens to the particles in a liquid or a gas when you heat them?
-The particles spread out and become less dense
Describe fluid movement
-Cooler, more dense, fluids sink through warmer, less dense fluids.
-In effect , warmer fluids (liquids and gases) rise up
-Cooler fluids (liquids and gases) sink.
Why is it windy at the seaside?
-The sea (at the left) is colder than the land
-The land (at the right) warms the air above it, and it rises
-The cold air from above the sea moves in to take the place of warm air that has risen (left to right)
Where is a freezer compartment put in a fridge and why?
-It is put at the top, because cool sinks, so it cools the food on the way down.
-It is warmer at the bottom, so this warmer air rises and a convection current is set up.
Describe radiation
-Radiation is heat waves, they travel in straight lines.
-Radiation can travel through a vacuum since it doesn’t require particles to travel
-Radiation travels at the speed of light.
Which color is the best at emitting and absorbing heat radiation?
Black
