Some microwaves may not reach their full power output when they are empty or have nothing inside them. This behavior is due to the way microwave ovens are designed and the safety features built into them.
Microwave ovens are designed to emit microwave radiation to heat food. When the microwave is empty, there is no food to absorb the microwaves, which can lead to a phenomenon called "reflected power." Instead of being absorbed, the microwave radiation bounces around the empty cooking chamber and can be reflected back into the magnetron—the component that generates the microwaves.
When too much reflected power goes back into the magnetron, it can lead to an increased load on the magnetron, potentially causing overheating and damaging the microwave's internal components. To prevent this, most modern microwave ovens are equipped with a safety feature called a "stirrer" or a "turntable."
Stirrer: Some microwaves use a stirrer—a metal fan-like device or reflector—that rotates with the microwaves' emission. The stirrer scatters the microwaves and helps distribute the energy more evenly throughout the cooking chamber. This prevents hotspots and reduces the amount of reflected power, allowing the microwave to operate more efficiently even when empty.
Turntable: Many microwaves have a rotating turntable at the bottom of the cooking chamber. When the microwave is in use, the turntable rotates, ensuring that the microwaves reach all parts of the food, and this also helps prevent excessive reflected power.
By incorporating a stirrer or a turntable, microwave ovens can achieve more uniform heating and prevent excessive reflected power when there is nothing inside the cooking chamber. These safety features not only protect the microwave's internal components but also help ensure safer and more efficient cooking when preparing food.