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boiling kettle

A watched kettle never boils

There is an old wives’ saying that ‘a watched kettle never boils’. There is an element of truth in this. The rate of heating of the water in a kettle starts quite fast and then slows down during the process before picking up again as the water starts to boil vigorously. The slowing down in the middle of the process can make it feel as if the kettle is never going to boil. It happens due to something known as the Leidenfrost effect.

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This article is from the free online course:

Energy: Thermodynamics in Everyday Life

University of Liverpool