QuestionWe have learnt about conduction.

What is another method of heat transfer which involves particles?

Think about the solid, liquid and gas particle models.

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solid liquid gas

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Can you explain how the convection current moves using the idea of density?

The movement of hotter areas in a liquid can be seen using potassium permanganate as a dye:

heat

This cycle is called a convection current.

heat

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ConvectionLike conduction, convection involved particles.

Convection occurs in fluids (liquids and gases).

Why is this? Why can convection not occur in solids?

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heatless dense

fluidThe heated fluid particles gain energy, so they move about more and spread out. The same number of particles now

take up more space, so the fluid has become less dense.

What happens to the particles in a fluid when it is heated?

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Therefore:

Energy is spread by the fluid expanding and rising as it is heated.

This causes the space between the particles to increase and therefore the density is said to decrease.

This movement of particles, rising and falling is creates a convection current.

ConvectionConvection cannot occur in solids because, as you know, the

particles in a solid are in a fixed and regular repeating pattern.

Remember – Vacuums have no particles so again, convection can not occur (nor can conduction).

Liquid and gas particles are able to move!

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ConvectionTask 1:

1. Draw a diagram and then explain why we have winds at the seaside.

2. Explain why the freezer compartment on a fridge is at the top.

REMEMBER – hot particles rise and not heat!

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Why is the freezer compartment at the top of a fridge?

The freezer compartment is at the top of a fridge because cool air sinks.

This warmer air rises and so a convection current is set up inside the fridge, which helps to keep the fridge cool.

The freezer cools the air at the top and this cold air cools the food on the way down.

It is warmer at the bottom of the fridge.

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ConvectionConvection occurs in liquids and gases.

This is when heated stuff moves in bulk to a cooler region and takes the heat with it. The movement creates a convection current.

Currents are created as fluids rise when they are heated (they become less dense – particles are more spread out). They then fall when they cool down (they become more dense – particles are closer together).

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ConvectionTask 1:

1. Answer questions 1 - 3 on page 235.

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Are you now able to….

I still feel unsure. I need some more help to understand.

I feel ok. I need to do some more work to check my understanding.

I am happy and feel I understand and can explain the main points.