Q: Given a scientific passage and an answer, generate a question for the given answer.
Passage: An electromagnetic wave begins when an electrically charged particle vibrates. The Figure below shows how this happens. A vibrating charged particle causes the electric field surrounding it to vibrate as well. A vibrating electric field, in turn, creates a vibrating magnetic field. The two types of vibrating fields combine to create an electromagnetic wave. You can see animations of electromagnetic waves at these URLs:. Answer: vibrating
A:
Electromagnetic waves are generally caused by magnetic fields doing what (or moving in what way)?