The propagation speed of electromagnetic wave in vacuum is equal to the speed of light,

The propagation speed of electromagnetic wave in vacuum is equal to the speed of light,

Light is a kind of electromagnetic wave. The speed of light in vacuum is 2.9989 × (10 ^ 8) m / s, that is 300000 km / s, so the propagation speed of electromagnetic wave in vacuum is 300000 km / s

The speed of light and the speed of electromagnetic wave
Light speed = 3 * 10 ^ 8km / S
Electromagnetic wave velocity C = 3 * 10 ^ 5km / S
But why are they equal?

You have the wrong number for the speed of light
Light speed = 3 * 10 ^ 8m / S
Electromagnetic wave velocity C = 3 * 10 ^ 5km / S = 3 * 10 ^ 8m / S
So it's numerically equal

Why is the speed of electromagnetic wave equal to the speed of light?

First of all, it is more accurate to say that the propagation speed of electromagnetic wave in vacuum is the speed of light, which is derived from Maxwell's equations in vacuum, i.e. wave equation. Second, field is a kind of material, which often represents an interactive medium. It is of little significance to talk about the velocity of field, but we can know from the delayed potential, including electromagnetic phenomena