[ELI5] How does a rice cooker “know” the timing to switch from cook to warm when there’s no more water in it?
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[obligatory technology connections video](https://youtu.be/RSTNhvDGbYI)
Tldr is that when you boil water it won’t exceed 100c at sea level. Cos all the energy goes into making the steam. Coincidentally there are magnets that reduce their strength at just over 100c. The magnet holds a contact closed allowing the cooker to heat. Whilst there’s still liquid water it won’t exceed 100c. Once all that water evaporates or is absorbed into the rice the heat rises to the temp the magnet becomes weaker (the curie temperature) the magnet looses strength and then disconnects the heater
Most of them use a super convenient property of magnets/magnetism, they tend to lose strength as temperature rises. So you just find a magnet that loses exactly the correct amount of strength at say 213° to release a switch and it will instantly cut off once all the water has boiled away.
It actually is quite ingenious how they use magnets and thermal knowledge. TC goes into detail here on how they work: [how rice cookers work](https://youtu.be/RSTNhvDGbYI)
There is an alloy that has the property of losing its magnetism when heated to a certain temperature. There is a magnetic latch that holds the spring loaded contactor closed, (if you look under the pot part of a rice cooker there is a springy plunger which works with the lever/button you use to start the cooker to bring the magnet in contact with the latch.) When all of the water is boiled away/absorbed by the rice the temperature of the cooker climbs above the temperature where magnetism is lost and catch is released breaking the circuit. When it cools down it regains its magnetism. It is really an amazing, simple, lucky gadget.
This is super interesting. The rice cooker boils the water. When water is boiled it doesn’t change temperature. It holds temp while it’s transitioning into steam. It’s only once all the water is boiled off that the temperature starts to increase.
So all the rice cooker has to do is wait for the temperature to increase before shutting off.
[Technology Connections has a great video on this exact topic!](https://youtu.be/RSTNhvDGbYI)
This video does a wonderful job explaining your exacting question: https://youtu.be/RSTNhvDGbYI
The most common temperature sensor is a common magnet. Once the water gets hot enough to boil, the energy being added starts to warm a magnet. That magnet will hold the switch in the “cook” position until it gets too hot and then the magnet weakens and the switch change to “warm”.
[This guy](https://www.youtube.com/watch?v=RSTNhvDGbYI) gives an *amazing* explanation of it. Basically it just keeps track of the boiling of the water with a mechanical mechanism. But I highly suggest the video.
Husband bought one when he was into rice.. I didn’t think we needed it. We ended up throwing it out, because it always scorched. Was it a bad one? I just make it on the stove & keep an half an eye on it. Comes out just fine.
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