電磁波係由電同磁組成?

Electromagnetic waves are oscillation of electric and magnetic FIELDS. Hence, its propagation is not affected by static electric or manetic fields.

However, in some situation, electromagnetic waves do affected by free charges, such as when travelling in plasma (an ionized gas) in which the speed and direction of the waves would be changed. An example is the refraction of radio waves by the ionosphere (an ionized layer at the upper atmosphere of the earth).