The two allowed microwave frequencies for use in a microwave oven are 2.45 GHz (Gigahertz) and 915 MHz (Megahertz). These frequencies are chosen for their ability to efficiently heat water molecules, which is the primary method by which microwaves cook food.
2.45 GHz: The vast majority of household microwave ovens operate at a frequency of 2.45 GHz. This frequency was chosen because it aligns with a resonance frequency of water molecules. When microwaves at 2.45 GHz are absorbed by water molecules in food, the molecules rotate rapidly, generating heat throughout the food item. This heating process is what cooks the food from the inside out.
915 MHz: While less common, some commercial microwave ovens and industrial applications may use a frequency of 915 MHz. Similar to 2.45 GHz, this frequency is also absorbed by water molecules, causing them to heat up and cook the food.
The reason for choosing these frequencies is that they offer good penetration into the food, allowing for more uniform cooking. It's important to note that these frequencies are tightly regulated by international standards to ensure that microwave ovens do not interfere with other wireless communication devices and to maintain safety limits for human exposure to microwave radiation. As a result, microwave ovens are designed and tested to comply with these standards to ensure safe and efficient operation.