An electrical appliance that creates simple life for busy metropolitan is the microwave oven. It cooks food in minutes with no flames, no smokes and no mess. How does a such oven cook food? It works on radio wave principle.
If you observe carefully, you will discover that a microwave oven is a box with five solid metal walls. The front door window area has a meshed metal grid. When the door is closed, radio signals cannot leave the box.
When a microwave oven is in operation, it transmits 2.4GHz radio waves within the metal box to "excite" the water (moisture) content within meat and vegetables. The "rubbing" of moisture content creates heat and hence warm or cook the food. In order to fully cook all sides of the food inside, the platform underneath rotate. Old microwave oven might have a fan at the top to "stir" the radio waves. As mentioned earlier, the meshed metal structure at the front door stops most 2.4GHz radio waves from leaving the box.
Why 2.4GHz radio waves? Radio waves above this frequency begins to resonate with the water content inside meat. It's certainly a clever invention.