How do electromagnetic waves form due to moving electric charge ?
Charges in matter is a physical property that helps identify the matter as what it is; it is one of the identifying characteristics of such. An electrical charge on a particle of a substance produces an electromagnetic field around it. These charges can be positive or negative. Like charges will repel each other, while opposite charges will attract each other. Differing strengths of electric charges will produce electromagnetic fields of varying strength, all of which will fit into the overall electromagnetic spectrum. It is not so much a matter of how does it happen as it is an established fact, a physical property that may be readily observed. Moving electric charges create electromagnetic fields around them, both of which may be measured, using appropriate electrical devices.