Convection (T4) Flashcards
What is convection?
Convection is the transfer of heat in a fluid by its movement in a cycle.
(By fluid we mean a substance that can flow, like a liquid OR gas)
Explain how convection and a convection cycle works..
When a gas or liquid is heated up the molecules move more quickly and so the volume will increase as they tend to move apart.
This will mean they occupy a large volume, decreasing the density of the fluid in the hot region.
A fluid that is less dense than its surroundings will start to move upwards.
However when a fluid rises to a higher location away from the heat source it will cool down.
The cool fluid will be denser again so it will then fall back down, after which it will replace the hot fluid that rose upwards initially above the heat source.
Thus, a complete cycle is formed which transports energy upwards, away from the heat source.
This is called a convection cycle OR convection current.
How do lava lamps use convection?
Lava lamps use two liquids that do not mix, one clear and one coloured.
As the coloured liquid at the bottom is heated, it expands.
As a result of the expanding, the coloured liquid becomes less dense so it floats to the top.
When it eventually cools it sinks back to the bottom.
How do convector heaters work?
Convector heaters heat air, which then floats out of the top of the heater to the top of the room.
Cold air is drawn in at the bottom and this in turn is heated.
In this way, heat energy is eventually transferred to all parts of the room.
