Dear Experts, When an electromagnetic wave moves from a rarer to a denser medium or gets reflected by a mirror, it encounters a phase shift of pi or (lambda/2), in that case, the reflected wave will be out of phase with the incident wave. I have a very basic (maybe non intuitive or even stupid) doubt regarding this. Does the above mentioned statement imply that a light wave incident at 0 degrees to the normal to a surface will be completely destroyed by its reflecting counterpart?. I am also finding it hard to understand why the phase shift occurs only in the interface between rarer to denser and not from denser to rarer. There are explanations in terms of waves on a tied string, but in case of electromagnetic waves in which fields are fluctuating, how can we relate the behavior. Thanking you in advance.