Please forgive this last piece of candle nonsense! After the talk last week the first questioner asked me:
“Why do candles burn for longer after you put them in the freezer?”
Frankly it wasn’t a question I was expecting. I did have the presence of mind to ask if she had compared the cold candles with some she had kept at room temperature.
She said, “No”, but she did say that when she took the candles out of the freezer they had “burned all evening”.
Faced with this experimental ‘fact’ I speculated that perhaps the flame lost some energy melting the colder wax. This seemed to satisfy the questioner, but I was not happy.
So the next night I put a candle in the freezer and after a couple of hours I burned it with a similar candle I had kept at room temperature: I could see no obvious difference.
And so this evening I conducted the definitive experiment. I had previously chilled a candle in the freezer and my (uncalibrated*) thermometer told me its temperature was -13.8 °C. The comparison candle was at room temperature: +18.4 °C. These temperatures should be compared with the melting temperature of wax which is typically 55 °C.
Both candles initially weighed 54 grams and I lit them quickly to maximise any cooling effect before the ‘cold candle’ warmed up.
Making measurements in the usual way it became apparent that the candles burned at nearly the same rate, and if anything, the ‘cold candle’ burned a little faster!
The three gram difference is only just resolvable with my weighing machine, but it corresponds to nearly 9 mm difference in height and as the photograph at the top of the page shows, the ‘cold candle’ is definitely shorter than the ‘warm candle’.
So what, I hear you silently wondering, is the point? The point is that I now know the answer to this question! And so do you. Experimental physics has answered one question and – as it frequently does – raised several more. For example: is the difference in burning rates really associated with temperature or was there some other variable I didn’t control. Perhaps another happy evening of experimentation will resolve this!
I love Experimental Physics, and when work is depressing or unsatisfying, the ability to definitively resolve such questions as this – pointless as they are – gives me considerable comfort.
*Sorry: At home I have to operate to much lower standards 😦