Monday, May 6, 2013

how does a kettle boil water, and what happens to the water particles?

electric kettle warmer
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i'm bored


i have figured out that the heating coil of an electric kettle is always placed at the bottom of the kettle to aid transfer of thermal energy in water by convection.

i know convection takes place, but what else? like conduction, radiation etc..
and what happens to the water particles, thank you so much for your answers everyone!



Answer
All matter (in our world anyway) has some measure of kinetic energy that we call heat. It's pretty complex, but you can imagine it as all these little atoms or molecules, each having some random velocity. The molecules bounce off of each other and transfer their energy from one to another. Individual atoms don't get warm, and they can't easily get rid of this kinetic energy, so something that's "hot" stays hot until it can give that energy away, either by colliding into other molecules, radiating it as energy, or having its hotter parts carried away. We call those phenomena conduction, radiation, and convection.

When you turn the heater on, electrons flowing in the element bash into the nucleii of the element's atoms, and send them slamming into each other. They also slam into the bottom of the kettle, conducting this energy into the kettle. The same thing happens when the kettle's atoms slam into the water molecules. Those heated molecules are like a mosh pit; at first, before the music starts, you can fit a lot of people in, but when they start smashing into each other, they have to spread out and some people get thrown or pushed out. Having lower density, the hot water molecules are pushed up to allow the denser cold water to come in contact with the kettle. This is convection.

The element and kettle, and even the water, give off electromagnetic radiation as their electric charges vibrate around. You can see this when the element glows orange, but it's happening everywhere else too, just at wavelengths you can't see.

Eventually all of the water in the kettle is heated to the boiling point, and the heat energy starts to exceed the hydrogen bond energy that holds the water molecules together. Now boiling starts. A great deal of energy is spent in overcoming these bonds, so the boiling takes place at exactly the rate of the energy entering the water. Those molecules that split off from the liquid water dissolve in the atmosphere as steam.



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