Two candles are lit in Ranga's room and immediately two containers, P made of glass and Q made of stainless steel, are inverted over them. After a few minutes the containers are lifted and Ranga...
- Two candles are lit in Ranga's room and immediately two containers, P made of glass and Q made of stainless steel, are inverted over them. After a few minutes the containers are lifted and Ranga finds the candle in Q still burning. What is the most likely reason for this?
The most likely reason for this is that the stainless steel container around candle Q is a much better conductor of heat than the glass container around candle P. A candle that burns steadily, which is often taken for granted, actually requires a complex balance of heat and mass transfer for everything to keep going smoothly. The right amount of oxygen needs to diffuse to the flame, and the heat from the flame needs to liquefy more wax at just the right rate to replenish the fuel source without dousing the flame out. An imbalance in this last factor is what I propose went wrong with candle P and not with candle Q. The heat insulating property of the glass in candle P caused the temperature of the contained air inside to rise rapidly due to the heat from the flame that had no where to go. This increase in temperature likely caused too much of the wax to melt at the top of the candle, essentially creating a deep puddle of wax that snuffed the flame. Either that or (if it was a thin candle) the wax softened and the structural integrity of the candle broke down, causing it to sag or fall over and stop the flame. Either way, extreme heat buildup around a candle will certainly put it out one way or another. Meanwhile, candle Q burned and generated just as much heat as candle P, however the heat was able to escape the container by conduction through the metal walls. Thus, the air temperature in container Q did not increase as rapidly as in container P and the over softening or melting of wax did not occur.
Another possible reason that the increase in temperature in container P could cause the candle to go out before the candle in container Q has to do with the rate of combustion of the wax. The rate of any reaction or mass transfer is usually a function of temperature among other things. Thus there is a chance that a higher temperature in container P allowed oxygen to diffuse more rapidly to the flame, resulting in an increased rate of combustion (candle flames are diffusion limited by oxygen). This would lead to more rapid oxygen consumption and within minutes the oxygen concentration inside of container P could have dropped too low for the flame to continue. Because the temperature remained lower in container Q (as discussed) this problem would not have occurred as quickly and the flame would remain.
I believe that the first option is more likely than the second, but they are both valid and both arise from the rapid temperature increase inside of the insulating (glass) container compared to that of the conducting (stainless steel) container.