# page 21 physics

page 21 convection-physics

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• Created by: Waldron16
• Created on: 16-11-13 18:09
What forms of matter uses convection of heat
liquids and gases
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How does convection occur?
Convection occurs when the more energetic particles move from the hotter region to the cooler region-and take their heat energy with them.
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Give the steps for how an immersion heater heats water up
see next flash cards for first step
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1. Heat energy is transferred from the heater coils to the water by conduction (particle collisions)
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2. The particles near the coils get more energy so they start moving around faster.
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3. This means there’s more distance between them i.e. the water expands and becomes less dense.
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4. This reduction in density means that the hotter water tends to rise above the denser, cooler water.
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5. As the hot water rises it displaces (moves) the coolers water out of the way, making it sink towards the heater coils
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6. This cold water is then heated by the coils and rises0and so it goes on.
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7. You end up with convection currents going up, round and down, circulating the heat energy around the water
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which objects is convection most effective in?
Note that convection is most efficient in round or squarish containers because they allow the convection currents to work best. Shallow wide containers just don’t work as well.
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If the heater coil in the immersion heater was in the middle, which parts of the tank would get hot?
Also note that because the hot water rises (because the lower density) you only get convection currents in the water above the heater. The water below the heater stays cold because there is almost no conduction.
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what are the main point to make when talking about convection currents in an exam?
Convection currents are all about changes in density.
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What other household appliance uses convection?
The radiator example Heating a room with a radiator relies on convection currents too. Hot less dense air by the radiator rises and denser, cooler air flows to replace it.
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exam question: how does convection work?
Water heats, Hot water less dense, less dense water rises, fast moving particles collide with slow moving particles and transfer heat, water cools and becomes more dense, denser water sinks again.
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## Other cards in this set

### Card 2

#### Front

How does convection occur?

#### Back

Convection occurs when the more energetic particles move from the hotter region to the cooler region-and take their heat energy with them.

### Card 3

#### Front

Give the steps for how an immersion heater heats water up

1

2