Q.1 Two progressive waves meet at a fixed point P. The variation with time of the displacement of each wave at point P is shown in the graph. What is the phase difference between the two waves at point P? displacement 0 0.1 0.2 0.3 04 0.5 0.6 0.7 08 0.9 -1.0 -1.1 1.2 -time/s O 180 O 1350 O 450 O 90