What causes microwave spark?

Chef's answer
Sparks in the microwave are usually caused by the microwaves hitting a metal object inside the appliance. Metals conduct electricity with lots of electrons which move freely. ... Sparks occur simply due to a build-up of charged particles which produce a concentrated electric field at the edge of the metal object.
Frequently asked Questions 🎓
Is a Sparking Microwave Dangerous? In most cases, you're perfectly safe if your microwave starts sparking. However, if you see sparks in the microwave, you should still turn it off immediately..
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