Nisreen Al Mugheiry Abrar Al Ghailani Shuruq Al Zawawi Convection Nisreen Al Mugheiry Abrar Al Ghailani Shuruq Al Zawawi

Warm-up In Chinese herbal tea shops, bowls of herbal tea are usually covered by glass plates. Why do the shop owners need to do this?

Warm-up Some freezers at supermarkets do not have doors. This is just opposite to what herbal tea shops do. What could be the reason?

Introduction Have you noticed... Air-conditioner is usually installed high on the wall immersion heater is fixed near the bottom

These have to do with the transfer of heat by convection. Introduction These have to do with the transfer of heat by convection.

Convection in water notice its movement Put a purple crystal into a beaker of water near the side. notice its movement

note the smoke's movement Convection in air Light the candle & hold a piece of smoking paper on the other side of the cardboard. note the smoke's movement

Convection current When the water is heated at the bottom, water expands, rises & is replaced by cold water from above.

Convection current The flow of water is called convection current. This method of heat transfer is called convection.

Convection current Similarly, when air is heated, air expands, rises & is replaced by cold air from above.  convection current

Why air-conditioners are usually set up high on the wall? Convection current Why air-conditioners are usually set up high on the wall? Warm air is taken in by the air-conditioner & cooled. An air-conditioner gives out cold air which falls. This pushes the warm air up. This results in a convection current.

Why crawl on ground during a fire?

Why crawl on ground during a fire? In a fire, why should you crawl close to the floor in a smoke-filled room? Smoke is warmer than the surrounding air. It rises & its places would be replaced by the surrounding cooler air. Smoke is toxic. We should crawl close to the floor to prevent smoke inhalation.

Convection current Heat can be transferred in a fluid (liquid/gas) by convection, in which the heated fluid expands, rises and is replaced by the surrounding cooler fluid. Such movement of fluid is called convection current.

Convection and particle motion In kinetic theory, particles in a liquid are close together. But they are not in fixed positions.

Convection and particle motion When a fluid is warmed, the fluid particles move faster  warm fluid expands  less dense than surrounding cold fluid  warm fluid rises  cool fluid from the top moves down to replace warm fluid  convection current

Examples of convection Wind and sea breezes Land and sea breezes over the coast in the summer are caused by convection current.

Examples of convection Wind and sea breezes warm air expands Warm air rises warm air cools wind During the day, the Sun heats up the land more quickly than the sea. cool air blows in from the sea to replace it

Examples of convection Shape of candle flame hot air rises Fire or flames always point upwards... since convection current flows upwards

Matters of which of the following states CANNOT have convection? A Solids B Liquids C Gases

Draw the convection current formed in water when we boil water.

When liquid/gas is warmed… When liquid/gas is warmed, the warmer liquid/gas expands and becomes _______ dense than the surrounding liquid/gas. Hence, it rises. less The surrounding cooler liquid/gas moves to replace the warm liquid/gas. Such liquid/gas movement forms a ____________ current. convection