Question

How is the speed of electromagnetic waves in a vacuum determined by electric and magnetic fields

Answer 1

Alternating magnetic or electric field result propagation in vacuum in form of electromagnetic waves. The speed of the electromagnetic wave was found to be 3 x 10^8 m/s. ... But anyway what it also does is that it says that when you change a magnetic field you generate an electric field.

Answer 2

The speed of E. M. Wave is given by the formula,

c= 1 / ε0μ0

Hence Velocity depends on medium not on strength of electric and magnetic field.