During the Junior Certificate Science course, you will have studied the three methods of heat transfer and demonstrations of each. These are conduction, convection and radiation (Fig. 11.8).
For the Leaving Certificate Physics course, you need only to be able to define each and give an accompanying experiment.
Conduction
Conduction is the transfer of heat energy in a solid by passing on kinetic energy from molecule to molecule.
To demonstrate conduction in various materials
1. Set up the equipment as in Fig. 11.9 with Vaseline on the end of each rod.
2. Stick a thumbtack to the Vaseline. 3. Fill the water bath with hot water (between 70° and 80 °C, so be careful).
4. The rod that conducts heat the best will melt the Vaseline fastest. The rate at which the Vaseline melts indicates the rate of conductivity of the material of which the rod is made. The order in which the thumbtacks fall off shows the relative rates of conductivity of the rods, from highest to lowest.
FIG. 11.9 Convection
Convection is the transfer of heat energy by the circulation oftheheated parts of a liquid or gas.
To demonstrate convection
1. Set up the equipment as in Fig. 11.10. 2. Drop the potassium permanganate using a filter funnel, to keep it in one place at the bottom of the water.
3. Heat the water and note how the potassium permanganate moves through the water with the convection currents.
FIG. 11.10 LEAVING CERTIFICATE PHYSICS 109 beaker water
potassium permanganate crystal
NOTE
Potassium permanganateturns purple in contact with water.
temperature probe
water bath
thumbtack vaseline
wood glass steel iron
aluminium cooper
radiation radiation
FIG. 11.8 The three methods of heat transfer: conduction, convection and radiation
