How do kettles boil water?

The electric kettle works thanks to two design breakthroughs
achieved in Britain in the Twenties and Thirties. The fi rst is the
immersed heating resistor, the piece of technology responsible
for actually heating the water in the kettle. Resistors, which take
the form of the heating element in the bottom of the kettle, work by
resisting the fl ow of electric current passed through them, creating
resistance and consequently heat. This heat is then passed into the
water, which is subsequently heated up. The second of these advances
allowed for an automatic cut-off point, preventing the kettle from
perpetually heating up the water. A bimetallic strip was introduced
to the electric kettle by Russell Hobbs in 1955 which when heated by
steam expanded, triggering a shut-off switch.
Although some kettles have fancier and
more complex heating and shut-off
designs, it is through these two basic
principles that the electric kettle
evolved into the appliance we have
in our kitchens today.