What is the function of the grating on the door of a microwave oven?

People using microwave ovens want to see the food cooking inside the oven, yet not be bombarded by potentially harmful microwaves. In order to prevent the escape of microwaves through the plastic or glass door, a grating consisting of small holes is used to reflect the microwaves back into the oven. The microwaves (which have a wavelength of about 12 centimeters [4.7 inches]) are too big to pass through the holes, but visible light, whose wavelength is smaller than the opening, can easily pass though the grating. Although the grating protects people from the microwaves, some microwaves can still leak out through the door seal, however, if it’s not cleaned occasionally.


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