I have to do a Phy. Project about rice cooker ...

A rice cooker or rice steamer is a device used primarily for cooking rice. There are self-contained electrical versions, as well as microwave, gas, and open flame variants.
Basic principle of operation
The bowl in the rice cooker is usually removable, and beneath it lie a heater and a thermostat. These form the main components of the rice cooker. A spring pushes the thermostat against the bottom of the bowl, for good thermal contact to ensure accurate temperature measurement. During cooking the rice/water mixture is heated at full power. The temperature cannot go above the boiling point of water -- 100°C (212°F) -- as any heat put into the rice/water mixture at that point will only cause the water to boil. At the end of cooking some of the water will have been absorbed by the rice and the rest is boiled off. Once the heating continues past this point, the temperature exceeds the boiling point. The thermostat then trips, switching the rice cooker to low power "warming" mode, keeping the rice no cooler than approximately 65°C (150°F). Simple rice cookers, like the one below, may simply turn off at this point.

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