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RADIATION EXPT.
RADIATION
Results:
Dark colours emit better than shiny or light colours.
CONVECTION
EXPANSION
The warm air heated by the candle rises. This causes the spiral to spin.
HEAT
CONDUCTION
CONVECTION CURRENTS
"Convection current"
The “lava” at the bottom is heated, expands, is less dense, so rises.
At the top it cools, contracts, is more dense, so sinks.
EFFECT OF HEAT
HEAT TRANSFER
4 credit internal
Heat can be passed from a hotter area to a colder area by 3 methods:
When a substance is heated several things might happen…
Convection
Conduction
Radiation
SUMMARY
Solids
Metals conduct.
Plastics and wood insulate.
particle vibrations passed through objects
Fluids (liquids and gases)
Convection current.
moving particles; area is heated , so expands, so is less dense, so rises, so cools, so more dense, so descends
Black emits and absorbs best.
Shiny reflects.
pure energy is emitted from one object, and another absorbs or reflects.
Transparent materials
Hotter particles move to a cooler place.
A hot object has particles moving fast.
A cold object has slow moving particles.
Particles vibrate to pass on energy.
Convection happens in fluids (liquids and gases).
Explain the results.
Warm objects emit (give out) radiant energy.
Conduct an investigation to find which colours emit radiation the best. Use the coloured cans and hot water. Make it a fair test!
Change in Temperature
As the particles are moving faster, they have more kinetic energy – we detect this as an increase in temperature.
Onshore/offshore breezes.
Warms faster
Cools faster
Change in State
If the particles have enough energy the bonds between them might break. This results in a state change, e.g. melting.
The warmer air cools as it rises, which causes contraction, and therefore it descends.
In a conductor, the particles are free to vibrate against other particles, so passing on their heat energy.
No particles. Pure energy is emitted from hot objects.
This means it will rise.
Warmer air expands, so it is less dense.
How well do other materials conduct?
Plastic Glass Water Wood
When particles in a solid are heated they vibrate.
This vibration causes the particles to take up more room.
This means the solid will expand.
Metals are generally good conductors.
Carry out an experiment to find out how metals compare in terms of conductivity.
It is made of 2 different metals. One expands more than the other. This results in the bending.
Heat the metal strip as shown.
Try to explain your observations, and how it can be reversed.
This has some far-reaching consequences in everyday life, such as:
Earthquakes, and continental drift and
How heat moves
Name
Where
Notes
Conduction
Convection
Radiation
Some objects absorb radiation well. Other objects reflect energy.
Which is which?
Here is a similar experimental set-up:
What did we find…
Ideally we would find that the Black/dull colours lose heat faster.
Often, though, we find it makes very little difference.
Why might that be?
This is called a Convection Current.
Cooler air comes in to replace it, and is heated and rises, etc.
Temperature is a measure of the average kinetic energy of the particles.
The unit for measuring temperature is °C.
Poor
These are called thermal insulators.
What makes a good conductor?
Change in Volume
As the particles speed up, they will take up more room (and become less dense).
When a substance is cooled the opposite occurs.
Dark objects
Shiny objects
Energy possessed by objects with particles that are moving.
Total of all of the particle's energy.
Measured in Joules (J).
Explain fully how the lava lamp works.