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THERMAL 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. Conduction by molecules. Molecules vibrate more when they are heated.

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THERMAL CONDUCTION

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  1. THERMAL CONDUCTION

  2. 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. web site: www.ktaggart.com

  3. 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. web site: www.ktaggart.com

  4. 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. web site: www.ktaggart.com

  5. 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. web site: www.ktaggart.com

  6. 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. web site: www.ktaggart.com

  7. 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. web site: www.ktaggart.com

  8. Air - a good insulator Air trapped in feathers, cavity wall insulation, loft insulation, duvets and lagging greatly reduces heat loss by conduction. web site: www.ktaggart.com

  9. 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. web site: www.ktaggart.com

  10. Question 2 Write down three insulating substances and three conducting substances as well as their uses in the table below: web site: www.ktaggart.com

  11. 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. web site: www.ktaggart.com

  12. Simulations Energy House Simulation. For instructions click here. web site: www.ktaggart.com

  13. Puzzles Conduction Crossword – by KT Sequential Puzzle onHeat Conductororder- by KT  - Microsoft WORD version Sequential Puzzle on Heat Conductor order- by KT - NOTE: Requires the use of SMARTBOARD software web site: www.ktaggart.com

  14. Related Presentaions Convection Powerpoint by KT Thermal Radiation Powerpoint by KT Evaporation Powerpoint by KT Heat Energy Transfer Powerpoint by KT web site: www.ktaggart.com

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