The electromagnetic wave is self propagating, what I mean by that is, an electric field generates a magnetic field at 90 degree phase angle, and the magnetic wave you get as a result generates the electric wave at the same phase angle. The interchange of electric to magnetic and vice versa continues and lets the electromagnetic waves to travel without any medium. Quite interesting, really!
A topic is the main idea of a writing. In this case, the topic of the essay is Yellowstone National Park because the essay talks about the national park itself.
It can get into the wrong hands.
