[填空题]
Two water waves $X$ and $Y$ travel on the same horizontal level as shown in the diagram.
The two waves have the same period of $3\,s$ and different amplitudes.
1.State what is meant by the principle of superposition.
2.At t=0 the two waves are just about to overlap.
(1)Sketch the wave pattern at $t=1.5\,s$.
(2)Sketch the wave pattern when the two waves completely overlap and name the type of interference that is occurring.
3.A wave with amplitude A is observed to have an intensity $0.42Wm^{−2}$ at a distance $0.5\,m$ from the source.
(1)Determine the intensity of the wave at distance $0.5\,m$ when the source amplitude $3\,A$. I = $Wm^{-2}$
(2)Determine the distance from the source at which the intensity is $0.84\,Wm^{−2}$ when the source amplitude is $3\,A$.
