Many practical classroom activities could be carried out, when teaching the concepts of conduction, convection, and radiation. These are simple yet relevant, and would allow students to understand the topic easily. The concept has to be taught in the first 15 minutes of the 1-hour class and then proceed to show some of these demos.
The teacher prepares the materials needed and see to it that safety precautions are observed.
- Prepare three different rods such copper, glass, and iron (or whatever is readily available, except of course plastic rods).
- Place them on a tripod and fix a small nail near one end of each rod using candle wax or Vaseline as ‘glue’. (Make sure the rods are not touching each other).
- Using a bunsen burner, heat the other ends of the rods evenly.
- Record the time it takes for each nail to drop off from the respective rods?
What happens after few minutes?
How many minutes does it take for the three nails to drop off?
Make a conclusion based on your observation and evidences.
- Put a beaker of water on a tripod.
- Prepare two pieces of potassium permanganate crystals.
- Using a drinking straw, drop the potassium permanganate crystal into the beaker of water, near to the side.
- With the Bunsen burner ready, warm the water near the crystal with a small Bunsen flame.
What happens to the crystal and the water?
What have you notice with the movement of the convection current in the
- Prepare two cans of equal size (with lid and a hole for the thermometer), one is polished and shiny on the outside and one is black and dull. ( You may use aluminium cans, paint the other one to make it black and dull)
Suggestion: It would be good too, to use boiling tubes with rubber bung and thermometer. One boiling tube is wrapped with aluminium foil, the other one wrapped with black paper.
- Put a thermometer in each and tip equal amounts of hot water.
- Let them cool, side by side.
- Stir regularly and record their temperatures every minute.
What do you observe with their temperatures?
Which cools down more quickly?
Which can, is losing energy quicker?
Which is a good absorber of radiation?
Concept: Objects take in and give out energy in the form of radiation all the time.
Different objects transfer different amounts of radiation, depending on their temperature and their surface. A dull black surface loses energy more rapidly and therefore it is good radiator. On the other hand, a brightly polished surfaces do not lose much energy by radiation, they are called poor radiator.
TRY THIS OUT!
- For conduction: Prepare a boiling tube with three-fourths water. Tilt it a little and hold it at the bottom. Aim a slow Bunsen flame just below the water surface until the water boils at the top.
Concept: Most liquids are poor conductor of heat. The water might be boiling at the surface but it could not warm up the liquid down below.
2. For convection: You may show convection current through smoke movement using a chimney box ( if available in your school).
3. For convection: Draw a spiral on a paper. Cut it out and hang it from a string or cotton thread. Use it to investigate convection currents by placing a lighted candle near the bottom.