Welcome you to this lecture and marine hydrodynamics. Today will talk about wave transformation and energy relations. So, there are various transformation when it comes to waves, so here will imprecise to two things; one is the scattering and radiation, and the other one is called radiation. So, what I mean I will also if time permits only I may talk too little about to the fraction if not today, may be in the next class. So, what I mean by scattering? We what that let me talk about three waves, what I mean by in coming wave and outgoing waves. In case of a incoming waves, suppose we have a observe bar here, in case of incoming wave the wave approaches towards the observer or towards or towards the struggle bar whatever it is, it can be approaching form either direction.