The speed that electromagnetic waves will travel within any medium is the same as those without a medium. The speed of electromagnetic wave is a constant and does not depend on the material of the medium.
Electromagnetic waves are waves that do not require a material medium for their propagation.
They are able to pass through vacuums and mediums with particles at constant speed.
It is mechanical waves whose speed is medium dependent.
Mechanical waves have varying speed based on the mediums they move through.
