If you drink coffee or tea by the bucket, you'll be glad someone once had the gumption to invent a super-efficient way of turning cold water into hot—namely, the electric kettle (also known as an electric tea kettle). Fill it with water, plug it in, switch it on, and in a couple of minutes you have piping hot water ready for drinking or cooking. How exactly does a kettle work? Why does it take so long to boil? And how does it know when to switch itself off? Let's take a closer look!

Kettles are among the simplest of household appliances. Lift the lid and peer inside and you'll see, at the very bottom of the water container, a coil of thick metal called the heating element. When you plug the kettle into an electrical outlet, a large electric current flows into the heating element. The element's resistance (the tendency any material has to stop electricity flowing through it) turns the electrical energy into heat. In other words, the element gets hot. Since it's in direct contact with cold water, the heat passes to the water by conduction and rapidly warms it up too.