Microwave ovens arc and spark with metal objects because metal reflects and conducts electricity. Microwave ovens work by emitting electromagnetic waves, specifically microwaves, which are a form of non-ionizing radiation. These microwaves are absorbed by food, causing water molecules in the food to vibrate and generate heat.
When a metal object is placed inside a microwave oven, it acts as a conductor of electricity. When the microwaves encounter the metal, they induce an electric current to flow through the object. This current can create sparks or arcs if the metal object has sharp edges, points, or gaps.
The reason for these sparks and arcs is that the high current density in certain areas of the metal can lead to concentrated electric fields. If these fields become strong enough, they can ionize the surrounding air molecules, causing a visible electrical discharge in the form of sparks or arcs.
It is important to note that arcing or sparking in a microwave oven is not safe and can potentially damage the oven or even cause a fire. Therefore, it is advised to avoid putting any metal objects inside a microwave oven unless they are explicitly labeled as microwave-safe, such as certain microwave-safe utensils or containers.