Electromagnetic Waves and Boundary Behavior

[dargahi]

I like to know if electromagnetic waves pass through a medium (Glass) and if this medium were in contact with two other mediums in its boundary which the first one with same optical dense (Glass) and the second with less optical dense (air).

Is there any tendency or priority for wave to pass from the same medium or not?

 

[sophiecentaur]

Not quite sure what you mean.
What 'priority' do you refer to? Would a diagram help, perhaps?
I can say that, whenever a wave passes across a change in medium, there is some reflection, whichever the direction of travel. The ratio between the two speeds is the refractive index (a term usually reserved for EM waves, actually but the same concept applies)