Question

What causes electromagnetic waves?

Answer 1

Acceleration of electric charges or transition of electrons between energy levels in atoms.

Explanation:

Either from accelerating electric charges example in a RLC ac circuit where electric charges change direction all the time and transmit the energy as an em wave and can be set to a required resonant frequency, etc. or from transition of electrons between energy levels in an atom example when an electron from a high energy level falls down into a lower energy level it releases the energy in the form of an em wave.