Convection of Heat in Air and Water

Convection of Heat in Air and Water

Everyday Science

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Let us learn convection of Heat in water
(1) Fill a beaker with cold water.

(2) Then carefully drop a few crystals of potassium permanganate to the bottom of the beaker.

(3) Now heat the base of the beaker by placing a Bunsen burner with a small flame under the flask and observe the crystals.

(4) When the water at the bottom of the flask is heated, it expands. The expanded water is less dense than the surrounding water and therefore starts to rise. The cooler regions of the water in the upper part of the flask, being denser, sink.

(5) Observe the coloured water rise up the beaker side, go across the top and then sink down the other side of the beaker — this is convection current.

Convection o Heat in Air

1. Take a closed rectangular box with glass fitted to its one side.

2. Pierce two holes at the top of the rectangular box.

3. Fit two glass tubes at the top to form chimneys.

4. Place the candle below chimney (B). Light the candle.

5. Hold the smoldering piece of paper over chimney A and observe the movement of the smoke.

6. You will observe smoke entering the box through chimney A and gets heated up by the candle and comes out of the chimney B.

7. This is because the air above the candle gets heated and expands and is now less dense than the surrounding air, it rises out of the chimney.

8. In doing so, the cooler surrounding air, being denser, sinks through the other chimney to replace the less dense air.

9. The movements of the hot and cold air set up a convection current .The smoke produced by a piece of smoldering paper held above the cooler chimney makes the convection current visible.