Yes, a metallic bowl can cause sparks when heated in a microwave oven. Microwave ovens work by emitting electromagnetic waves that excite water, fat, and sugar molecules in food, which generates heat and cooks the food. When microwaves encounter metal objects, they can reflect off or get trapped within the metal, leading to a concentration of electrical energy.
If the metallic bowl has sharp edges, creases, or is crumpled, it can act as an antenna and create concentrated electric fields. When these fields become strong enough, they can produce electrical sparks between the metal surfaces, leading to potentially damaging effects, like arcing and fire.
For safety reasons, it's essential to avoid putting any metal objects, including metallic bowls, in a microwave oven. Always use microwave-safe containers made of glass, ceramic, or microwave-safe plastic to avoid potential hazards and ensure the safe operation of your microwave.