When you use a microwave to heat food, it emits electromagnetic waves, specifically microwaves, which penetrate the food and cause the water molecules within it to vibrate rapidly. This molecular motion generates heat, which warms up the food.
After the microwave finishes its heating cycle and you open the door, you might not immediately feel the intense heat you expect. This is because microwaves work by heating the water molecules in the food, and the heat generated is primarily concentrated within the food itself, rather than the air or the interior surfaces of the microwave oven.
The air inside the microwave oven and the oven's interior surfaces do get warm during the heating process, but they are not heated to the same extent as the food. Additionally, the microwaves are no longer being emitted once the oven stops, so there is no ongoing source of heat production.
When you open the microwave, the heat stored in the food begins to dissipate into the surrounding air and the cooler surfaces of the oven. As a result, the temperature inside the microwave quickly starts to decrease. The air inside the microwave oven does not retain the heat as efficiently as the food, so it cools down relatively quickly. This is why you may not feel an immediate rush of hot air when you open the microwave.
However, it's important to note that the food itself is still hot after you remove it from the microwave, so it should be handled with care to avoid burns. The rate at which the food cools down will depend on various factors such as its initial temperature, thermal conductivity, and ambient temperature.