Microwaves use high-frequency radio waves to cook food much faster than conventional cooking techniques. While microwaves can be really useful for those looking to speed up cooking times, their unique method of heating food also has limitations. For example, running a microwave without anything in it will damage the microwave.
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Running on Empty
A microwave uses a magnetron tube to create the electromagnetic radio waves (better known as microwaves) that cook your food. These waves cause the water molecules within food to vibrate, which creates friction in the food that then turns to heat.
When a microwave runs without anything inside, or if an item contains no water molecules, the microwaves in the machine will be redirected into the magnetron. When the magnetron begins to absorb as many microwaves as it produces, it can be damaged.
No Magnetron, No Microwaves
Since running your microwave without anything inside may damage the magnetron, it's advised to avoid this at all times. Without a magnetron, your microwave will no longer heat your food properly, if it heats it at all. When the magnetron breaks, you'll need to repair or replace your microwave.
Don't Beat Yourself Up
If you run your microwave while empty for only a few seconds, it will probably be fine. This is particularly easy to do on some models that start running as soon as the door is closed if there's time left on the clock. If the magnetron is suffering damage, you'll probably notice a slight burning smell even before any real damage occurs. The amount of time a microwave can run while empty before suffering damage will vary based on the device and may sometimes occur after only a few seconds but sometimes as long as five minutes.
If you're not sure if your microwave has been damaged, you can test it by putting a microwave-safe container with water inside and then running it for a minute. If the water isn't hot, the microwave has been damaged. If the microwave still heats, it hasn't been damaged and can still be used safely.
What to Keep Out of Your Microwave
Never microwave dry foods that contain little to no water as the lack of moisture is similar to running the microwave dry. Also, never put metal in the microwave as the metal reflects and scatters the radio waves, creating a charge that will, in turn, create its own radio waves that will then interfere with the original waves.