Plastic and metal react differently in a microwave oven due to their different electrical properties and molecular structures. When microwaves are generated, they pass through the microwave-safe materials, but they interact with them in distinct ways:
Plastic: Plastics are composed of long chains of molecules called polymers. These polymers contain polar groups that can rotate and align themselves with the microwave's electric field. When microwaves pass through plastic, they cause these polar groups to rotate rapidly, generating heat in the plastic. As the heat increases, the plastic can reach its melting point, leading to deformation or melting.
Metal: Metal objects in a microwave oven do not contain polar molecules like plastics do. When microwaves encounter metal surfaces, the microwaves' electrical field induces electric currents in the metal. These currents flow through the metal, and because of its electrical conductivity, the metal rapidly dissipates the electrical energy as heat. This process can cause the metal to become extremely hot and potentially cause arcing (sparks) in the microwave.
Microwave-safe plastics are designed to withstand the heating effects caused by microwave radiation, but not all plastics are microwave-safe. Non-microwave-safe plastics can melt, warp, or release harmful chemicals into food when exposed to microwave radiation.
It is crucial to use microwave-safe containers and avoid using metal objects inside the microwave to ensure safe and efficient heating. When in doubt, always check the manufacturer's instructions or labels on the plastic containers or packaging before using them in the microwave.