P6: Transfers of Thermal Energy

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One experiment:

Prepare a few rods made from different materials

Use wax to attack small pins to their ends

Afterwards heat the end of the rods

Thermal energy will be transferred by conduction from one end to another

Of course, gradually the wax will melt and the pin will fall off

Best conducting rod will have the pin drop the fastest because it transfer the thermal energy the fastest

In any solid the particles are fixed in a regular structure and they cannot move

When the solid object is heated, the particles gain thermal and kinetic energy. Since they cannot move, they vibrate itself

When the particles with more kinetic energy vibrate, they pass the vibration to other particles as well

So the thermal energy is passed on!

Non-metals: when something is supplied with heat, its atoms vibrate faster and pass these vibrations to adjacent atoms

Metals: Same thing except there are some mobile electrons which travel randomly and collide with atoms and pass the vibrations

Convection is the main method of heat transfer in fluids

If the bottom of, let's say a glass filled with water, is heated, then the water above the heat will become warmer. The more warm it gets, it expands and decreases in density. The less dense water rises as cooler, denser water sinks and takes its place or displaces it. This is an example of a convection current.

Radiation is a method of heat transfer that doesn't require a medium to travel through

They can travel through everything, even empty space!

Experiments to show the properties of good and bad emitters

Infrared radiation (which is part of the electromagnetic spectrum) is often involved in heat transfer by radiation

Applications:

Solar panel: the sun's thermal radiation is absorbed by a matt black surface and warms up the pipes containing water

Refrigerator: At the top of the fridge, this is where the freezer department is located. It cools down the air which sinks. Any warm air goes to the top and is cooled. This creates a convection current which maintains a cold temperature

Metals in cooking ware: Conduct heat well

Consequences:

A metal spoon in a boiling water will warm up since it conducts heat

Convection currents create sea breezes. During the day when the land is warmer, it acts as a heat sources. However during the night, the sea acts as the heat source

Conduction

Convection

Radiation

Consequences of Energy Transfer