Transfer of Thermal energy

• Thermal conductors


  Solids which easily transfer heat
• Thermal conductors


  • Metal pan
  • Ceramic tea cup
• Thermal insulators (also called insulators)


  Solids which do not transfer heat well
• Thermal insulators


  • Woolen blanket
  • Layers of cardboard or paper
• Comparing conduction in tiles and textiles


  1. Find a tiled or stone area of floor

  2. In the same room leave a rug or bath towel (not a thin cloth, it must be thick)

  3. The textile must stay in place on the floor for several hours to ensure they are at thermal equilibrium (the same temperature)

  4. Stand with bare feet (hands can be used)

  5. Place one foot on the tiles or stone area, and the other on the textile (towel or rug)

  6. Observe the apparent temperature of the two materials as felt through the feet
• It will feel as though the tiles are cold while the rug is warm, however, they are at exactly the same temperature
• Tiles and stone


  Good conductors of heat
• Textiles such as rugs

  Good insulators, meaning they are poor conductors of heat
• Comparing conduction in wood and paper

  1. A cylindrical rod made of half wood and half metal is wrapped tightly in paper

  2. Using a gentle flame, and holding the rod clear of the top of the flame, gently heat the paper at the join of the wood and metal

  3. Turn the rod so that the paper is well-heated all around the circumference of the rod

  4. Stop when the paper is clearly discoloured

  5. Remove the rod from the flame, gently unwrap the paper and observe the burn pattern
• A distinct pattern is seen; where the paper touched the metal surface it is undamaged, where the paper touched the wood surface it is charred
• Metal


  Good conductor of heat
• Wood


  Good insulator, meaning it is a poor conductor of heat
• Demonstrating different rates of thermal conduction in metals

  1. The apparatus consists of 4 different metal strips of equal width and length arrange around an insulated circle

  2. Ball bearings can be stuck to each of the strips and equal distance from the centre, using a small amount of wax

  3. The strips should then be turned upside down and the centre heated gently using a candle, so that each of the strips is heated at the point where they meet

  4. When the heat is conducted along to the ball bearing, the wax will melt and the ball bearing will drop

  5. By timing how long this takes for each of the strips, their relative thermal conductivities can be determined
• With two of the demonstrations above (the rug & tiles and the rod made of wood and metal) students often get confused, as the result may 'feel' as though it is the wrong way round
• The more heat is taken away, the cooler something will be. That is why the paper doesn't burn when it is next to the metal (although usually everyone guesses that it will!)
• The more heat is held in by a layer of insulation, the more heat remains, which is why rugs and carpets help your feet to feel warm