A candle is placed in a tube filled with air but cut off from the external atmosphere by a water bath near the bottom of the tube, and a cork in a hole on top of the tube,as seen in the photograph at the left below.
The water is level is equalized inside and outside of the tube by removing and replacing the rubber stopper at the top of the tube. With the water level set, a hot filament, shown in the photograph at the right, lights the wick of the candle. (Pushing the switch on the power supply box at the left creates a current that heats the wire.) The candle will burn for a while and then go out, due to lack of oxygen, which is consumed in the combustion process. The question this week involves where the water level in the tube will be after thermal equilibrium is reached following the extinguishing of the flame. One way to describe the situation is to describe how much of the volume of the air now in the tube might be taken up by water - what percent of the tube initially filled with air will be filled with water. For example, a water level of zero percent above the bottom means that it is the same as before the candle was burned. Twenty percent means that 20% of the original air in the tube is replaced with water, 50% means that half of the tube is filled with water, and 100% would mean the the tube is entirely filled with water.
After the flame goes out and equilibrium is attained:
Click here for Answer #140 after February 24, 2002.
