How does an electric cooker work? --- Niraimathi, Madurai, India
There are two different kinds of "cookers". Things like electric griddles or "George Foreman Grills" keep a surface at a certain temperature (e.g. 400 degrees F). They do this using a basic thermostat that turns the heating element on and off.
The other type of cooker is something like a "rice cooker" or an "egg cooker". These cookers boil water as part of the cooking process. Once the water boils off (in the case of egg cookers) or gets fully absorbed (in the case of rice cookers), the cooker turns itself off or switches to warming mode. These work by testing the temperature of the pot. When it rises significantly above 212 degrees F, a temperature sensor detects it and switches modes.
If you would like to see the heating element and electronics used in a cooker like this, see: How Coffee Makers Work