Conduction THERMAL CONDUCTION
Definition of Thermal Conduction This is how heat energy flows from a hot to cold region of a substance without the molecules of the substance moving from the hot to cold region. July 2005 web site: www.ktaggart.com
Conduction by molecules Molecules vibrate more when they are heated. Intermolecular forces allow the molecules to pass their vibrations from one to another. The stronger the forces the faster the vibrations are passed. Solids are therefore the best conductors and gases the worst. A very poor conductor is called an insulator. A vacuum does not allow conduction. July 2005 web site: www.ktaggart.com
Conduction through metals Metals have an additional method of conduction. Metals have electrons that can move from one atom to another. These free electrons can pass energy through the metal very quickly. Most of the best conductors are metals. However, diamond, a non-metal, is the best conductor despite only using the molecule to molecule method. July 2005 web site: www.ktaggart.com
Finding the best conductor All the rods have the same length and cross-sectional area. They are all heated equally at one end with the bunsen burner. When the other end of a rod reaches a certain temperature the paraffin wax melts and the match stick falls off. A match stick will fall off the best conductor first. This should be the rod made of copper. July 2005 web site: www.ktaggart.com
web site: www.ktaggart.com Comparing brass & wood The gummed paper singes and burns first on the wood side of the rod. This is because the brass removes the heat away from the paper more quickly than the wood. Brass is therefore the better conductor. July 2005 web site: www.ktaggart.com
Water - a poor conductor A boiling tube of water is heated near the top of the water. Water boils at the top. The bottom of the tube remains cool enough to hold. This shows that water (and glass) only conduct heat relatively slowly. July 2005 web site: www.ktaggart.com
web site: www.ktaggart.com Air - a good insulator Air trapped in feathers, cavity wall insulation, loft insulation, duvets and lagging greatly reduces heat loss by conduction. July 2005 web site: www.ktaggart.com
web site: www.ktaggart.com Question 1 Choose appropriate words to fill the gaps in the paragraph below: Conduction is the main form of ______ transfer in solids. This is because the molecules are relatively _______ together. Extra heat energy makes the molecules __________ more. They pass on their extra vibrational energy to neighbouring ______________. Metals are __________ conductors of heat energy because they contain many free __________ which can move through the solid and ____________ energy. The electrons give up their energy when they ___________ with other molecules. July 2005 web site: www.ktaggart.com
conductor or insulator Question 2 Write down three insulating substances and three conducting substances as well as their uses in the table below: substance conductor or insulator use July 2005 web site: www.ktaggart.com
web site: www.ktaggart.com Question 3 Explain why newspaper wrapping keeps hot things hot, e.g. fish and chips, and cold things cold, e.g. ice cream, fur coats would keep their owners warmer if they were worn inside out, a string vest keeps a person warm even though it is a collection of holes bounded by string, a concrete floor feels colder than a carpeted one even though they are at the same temperature. July 2005 web site: www.ktaggart.com
web site: www.ktaggart.com Simulations Energy House Simulation. For instructions click here. July 2005 web site: www.ktaggart.com
web site: www.ktaggart.com Puzzles Conduction Crossword – by KT Sequential Puzzle on Heat Conductor order- by KT - Microsoft WORD version Sequential Puzzle on Heat Conductor order- by KT - NOTE: Requires the use of SMARTBOARD software July 2005 web site: www.ktaggart.com
web site: www.ktaggart.com Related Presentaions Convection Powerpoint by KT Thermal Radiation Powerpoint by KT Evaporation Powerpoint by KT Heat Energy Transfer Powerpoint by KT July 2005 web site: www.ktaggart.com