Convection

Conduction Thinking about keeping our beaker of hot water warm for longer… What could we do to reduce heat loss due to conduction?

Starter Should the radiators in our homes or classrooms be called radiators? If not what should we call them?

Lesson Aims To be able to explain convection using ideas of density and the particle model. To describe applications of convection e.g. heaters, sea breezes.

Homework Convection banding homework. These are long answer questions, you should plan and then write your answer. Useful words (copy into back of book) Thermal energy, particles, contact, density, expands, contracts, vibrates, vibrations, Due in by end first break Thursday

Demos Potassium Permanganate Smoke box Glitter lamp

Convection Transfer of heat energy in a fluid (liquid or gas) When the fluid is heated the particles gain kinetic energy. They move further apart (fluid expands)

Density Density is a measure of how heavy something is for its volume. e.g. lead is dense and has a relatively large mass in a small volume. Polystyrene is not dense – it has a small mass for quite a large volume.

Convection The expanded fluid is less dense so it will rise and the colder, more dense fluid surrounding it will fall to fill it’s place. If the heat source is still there, the colder fluid is heated, expands, rises and colder fluid falls to take it’s place. This cycle leads to a convection current.

Explaining Convection Title ‘Convection’ Copy the diagram into your book Stick sheet into your book and number the sentences in the correct order.

What happens here? Using ideas of heating, kinetic energy, expansion, density, convection current explain in 3 sentences how the above occur.

What happens to gas if we heat it? As the gas is heated, the particles move more _______. This causes the particles to move _____ apart. This means that the volume of the gas ________. This causes the density of the gas to decrease. This causes the gas to rise.

Convection As a gas or liquid is heated, the particles move more quickly. This causes the particles to move further apart. This means that the volume of the gas or liquid increases. This causes the density to decrease. This causes the gas or liquid to rise.

Can you explain these pictures?

Sea Breeze During they day, the land is warmer than the sea. The warm air over land expands and rises. It cools over the sea and returns to the land. This provides a refreshing sea breeze which is very welcome on a hot day. 

Conduction or convection? Use your knowledge of particles to explain why heat energy cannot transfer through a solid by convection but it can in a liquid or gas.