30 Aug 2020
If you’ve ever stayed home alone (at least as a high school student), you know that the microwave is a blessing, almost a gift from science; whether it be heating leftovers, whipping up a quick meal from those ready-to-eat meal packets, or even complementing your movie time with a pack of microwaveable popcorn, the microwave oven has always got you covered.
However, if you’ve ever used the microwave, you must also be aware of the rule of thumb that you never put metal objects in the microwave: ensure that you accidentally didn’t leave in a metal spoon or put in a metal bowl into the microwave!
This may seem extremely confusing at first; a microwave oven is made of metal itself – look at its inside walls to catch a clear glimpse of the metal! Why can’t we put metal in the microwave, then?
To answer that, we’ll first have to understand how a microwave oven heats food first. Microwaves are a form of electromagnetic radiation, but despite their prevalence in our kitchens, potential exposure to them can be harmful as it can heat your body tissues just as it heats food. Thus, the doors and external coverings of the microwave oven ensure that the microwaves don’t escape and cook you.
The metal inside (because metals are good conductors of electricity) also reflects the microwaves inside the oven and focuses them on the food that needs to be cooked. The molecules of food absorb the microwaves and then move back and forth to generate heat to cook/heat itself.
Aha! This is where the problem comes in – the reflection of microwaves by metal objects. When you leave a metal spoon or fork in the microwave, it, too, reflects microwaves. If there isn’t enough material in the microwave oven to be able to absorb the reflected microwaves from that spoon or fork, a mini bolt of lightning can be generated from the arcing between the metal object and another part of the oven.
While this mini bolt of lightning is not always very dangerous, it could potentially start a fire, damage sensitive electrical components, or ruin the microwave altogether. Therefore, it is best practice to avoid putting metal objects in the microwave oven to prevent damage of any form.