Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: jeffaziz on 23/03/2009 09:30:01
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jeffaziz asked the Naked Scientists:
Chris,
Couldn't be a bigger fan of the show (http://www.thenakedscientists.com/HTML/podcasts/); it's gotten me through many a blue morning.
My question is as follows: I'm a tea drinker (partial to Darjeeling, but Typhoo will do in a pinch). At the moment, our kitchen is being re-modeled and we lack a gas range. My wife bought us a lovely electric kettle; it boils water about twice as fast as I could do on the stove top.
The interesting fact about it is this: it makes a surprising amount of noise, a sort of rushing, crackling sound. Now, the kettle has no moving parts (well, the power switch). It seems clear that it must heat the water by electrical resistance. Where does the noise come from?
I mean, it must result from the heating of the water, but what's the physical mechanism behind all the racket?
Thanks,
Jeff Aziz
University of Pittsburgh
What do you think?
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When you heat water on the stove, the layer at the bottom is the first to boil, meaning it turns into a gas. The water vapor collects into bubbles, which rise toward the surface, passing through cooler water en route. The lower temperature causes the vapor to recondense into liquid and the bubbles collapse, making a noise. This gets gradually louder, as bubble production increases, until the water is so uniformly hot that the bubbles make it to the top without popping. At this point the noise diminishes. But it takes a moment before the vapor pressure builds up sufficiently in the top of the kettle to make it start whistling...
It's not like electrical imbalance in the kittle
Regards
Raghu
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Listen to the answer to this question on our podcast. (http://www.thenakedscientists.com/HTML/podcasts/show/2009.05.17/)