3.2 To discover the properties of materials  (Page 2/3)

Give another FIVE examples, each with a short explanation.

1.___________________________________________________________________

_____________________________________________________________________

2. ___________________________________________________________________

_____________________________________________________________________

3. ___________________________________________________________________

_____________________________________________________________________

4. ___________________________________________________________________

_____________________________________________________________________

5. ___________________________________________________________________

_____________________________________________________________________

4.2 Convection:

• Convection causes water to rise when heated.
• Convection causes water to sink when it cools.

ASSIGNMENT 6: TO ILLUSTRATE HEAT-EXCHANGE DUE TO CONVECTION

Requirements: Pyrex beaker

Glass tube

Burner

Cold water

Potassium permanganate crystals

• Fill a wide Pyrex beaker with cold water.
• Drop a potassium permanganate crystal through a dry glass tube to the bottom of the beaker. Make sure that the crystal is close to the side of the beaker.
• Place your finger firmly over the top of the tube and slowly lift up the tube.
• Heat the beaker slightly - right under the crystal.

What do you observe?

1. What is the colour of the crystal?

_____________________________________________________________________

2. What happens to the coloured water around the crystal when the heating begins?

_____________________________________________________________________

_____________________________________________________________________

3. What happens to the coloured water near the surface?

_____________________________________________________________________

THE APPLICATION OF CONVECTION IN EVERYDAY LIFE

• Ventilation in a room

When the windows are opened on top and below the hot air leaves the room through the top windows and fresh cool air enters through the lower windows.

• Cooling units

In fridges, the freezer pipes are situated at the top. The cold air descends and cools the whole fridge.

• Heating of liquids.

When a kettle with water is placed on a warm stove plate the liquid is heated by means of convection.

• Cooling of machines.

Motorcar engines are cooled with water that circulates around each cylinder. By means of convection assisted by the water pump the hot water circulates to the top tank of the radiator. In the thin pipes of the radiator heat is radiated out to the air. The water in the bottom tank is therefore colder than the water in the top tank.

• Land and sea breezes.

During the day the land becomes hotter than the sea. The air over the land also becomes warmer and rises. Cooler air coming from the sea takes the place of the warm air. This is how a sea breeze occurs.

Give another two examples of convection. Explain what is happening.

1.___________________________________________________________________

_____________________________________________________________________