How will the speed of propagation of an electromagnetic wave change during the transition

How will the speed of propagation of an electromagnetic wave change during the transition from a vacuum to a certain medium?

The speed of propagation of electromagnetic waves depends on the electrical and magnetic properties of the medium. In a vacuum, it is equal to c = 1 / (the square root of the product “mu_zero” by “epsilon_zero”). When passing into a certain medium, the speed of an electromagnetic wave can be expressed by the formula v = 1 / (the square root of the product “mu” by “epsilon” by “mu_zero” by “epsilon_zero”). Thus, the speed of propagation will decrease when passing from a vacuum to a certain medium (it will become less (the square root of the product of “mu” and “epsilon”) times).