Covering your dish while microwaving can help reduce radiation exposure for those standing nearby, but it's important to understand the type of radiation involved and how microwave ovens work.
Microwave ovens use a form of electromagnetic radiation called microwaves to heat food. These microwaves are non-ionizing radiation, which means they don't have enough energy to remove electrons from atoms or molecules and cause ionization. Therefore, they are considered generally safe for heating food.
When you microwave food without a cover, the microwaves penetrate the food and cause the water molecules inside to vibrate, generating heat. Some of the microwaves can bounce off the food and escape into the surroundings. While the amount of microwave radiation that leaks out is generally very low, covering the dish can help minimize this leakage and reduce exposure to any stray microwaves.
If you cover your dish while microwaving, it acts as a shield, trapping the majority of the microwaves within the enclosed space. This reduces the amount of radiation that can escape and therefore lowers the potential exposure for those standing nearby.
Regarding the vent hole on top of the cover, it can have an impact on radiation exposure. If the cover has a vent hole, it allows some of the trapped microwaves to escape, reducing the effectiveness of the shield. However, the amount of leakage through a small vent hole is typically minimal and may not significantly affect the overall radiation exposure.
It's important to note that modern microwave ovens are designed with safety features and built-in shielding to prevent excessive radiation leakage. As long as the microwave is in good working condition and not damaged, the risk of harmful radiation exposure is very low, even without covering the dish. Nevertheless, using a cover can provide an additional layer of protection, especially if you have concerns about radiation exposure.