Question

Reflection from denser to rarer medium cause phase difference laging

Answer 1

hey mate ur ans
Not all reflections have 180∘180∘ phase change, it depends on whether it's free end (denser to less dense medium) or fixed end (less dense to denser medium).
Water waves reach the shore cliff do reflect on the same phase so the amplitude near the wall is reinforced by reflection. The particles are free to moving up and down at the wall and hence the momentum is preserved in direction.
However for fixed end, the particles are locked in position, the reaction force acts in opposition direction so that the momentum flips its direction.