I'd like to know what formula to use in order to find the following : Imagine a uniform magnetic field. I am moving with a constant velocity perpendicularly through it. Do I see only an electric field? A magnetic field? Both? Or both of them? What if I move in the sense of the magnetic field with a constant velocity? What if my velocity changes with time? What if, instead of the magnetic field, it's an electric field? I do not expect the answer to all these questions, rather I'd like a formula to check it out myself. But if you have to say a word or even give the answer, I'm all ears. Thanks in advance.