If you have wondered how electric rice cookers know when to stop cooking, the engineering behind that is some of the most minimalist brilliance I’ve seen, brilliance that keeps the cost of these appliances down to ridiculously cheap levels.

So 2 high school physics concepts to revise before we understand this
1. Latent heat of water - you can raise the temp of water pretty quickly to close to 100C but then it takes extra heat to actually get past 100 cos of the energy required to actually turn water into vapour

So you can observe this by bringing some water to a boil and checking its temperature. It will rise to 95-96 at a reasonable pace and then slow down because as long as there is liquid water left in the vessel, the temp can’t go above 100C

The second concept is the Curie temperature - some magnetic materials lose their magnetism at high temperatures, and electric cookers use an alloy whose curie temp is just above the boiling point of water

So you combine these ideas and use a magnet made of this alloy connected to a spring and what happens is that the moment all the water has been absorbed by the rice, it’s temperature will start going above 100C (cos of concept number 1)

And the moment that happens, our alloy loses magnetism and plops back down disconnecting the heating element from the vessel. Job done. As always, no category of engineers makes me drop my jaw as regularly as electrical engineers.

And since this thread blew up - might I recommend that you pick up my book, which explores the basic science of Indian cooking - Masala Lab: The Science of Indian Cooking https://www.amazon.in/dp/0143451375/ref=cm_sw_r_cp_api_fabc_Cds9FbCT5VDM9