At the bottom of the kettle is a sealed electric heating element. Above the heating element is a canister that holds water. The canister can be removable, or it can be built into the kettle. The controls are on the side of the kettle. Typically, there is an on/off switch and a thermostat which controls how hot the kettle gets.
Electric Kettle Basics
The Heating Element
Electric kettles are powered by a heating element which works in the same way an electric range does. The heating element is a resistor—a material that resists the flow of electricity. When electricity flows into the resistor, it is turned into heat. That heat is what heats up the water inside the kettle.
The heating element is controlled by the thermostat. The thermostat has a variable resistor inside. The higher you set the temperature, the lower the resistance is. A small current runs through the thermostat, usually controlling an electronic switch called a transistor. The transistor, in turn, controls the heating element. When the resistance goes up in the thermostat, less current flows through, which causes less current to flow through the heating element. This keeps the heating element and the water cooler. When the resistance is reduced, the current through the thermostat increases, which causes the transistor to increase the current through the heating element. This raises the temperature of the water.