Question

If you were designing a room in a house, where would be the better place to put a heater, near the floor or near the ceiling? Why? Consider your answer in the context of convection.1. Near the ceiling, because the air warmed by the heater would quickly spread down and across the room, replacing the cold air.2. Near the floor, because the heater would warm the air close to it. After being heated, the now-warm air would rise, and be replaced by cool air, which the heater would warm. The cycle would continue until the room is heated.3. Near the ceiling, because the heater would warm the air close to it. After being heated, the now-warm air would descend, and be replaced by cool air, which the heater would warm. The cycle would continue until the room is heated.4. Near the floor, because the air warmed by the heater would quickly spread up and across the room, replacing the cold air.

Answer 1

Answer: The correct explanation is 2.

Explanation: The warm air is less dense (it expands) and thus it is lighter than the cold air so it will rise up to the floor. Therefore, when you place the heater on the floor it will warm the cold air which would then rise and be replaced by more cold air which would again get warm and rise and so on until the room is heated. This means that the correct explanation is 2.

On the other hand, if you put the heater at the ceiling, it will warm the cold air near the ceiling which would stay up there (it is lighter than the cold air under it). This means that the only way for the heat to spread from this ceiling level warm air to the lower levels is via conduction which is slow.