[填空题]
A speaker emits sound towards a tube that is open at both ends as shown in Figure A. The speed of sound is $340\,ms^{−1}$ and a standing wave is formed in the pipe. At a particular instant, the positions of particles X and Y are shown.
Figure B shows the displacement of molecules of air in the pipe at this instant in time. Displacement to the right is positive.
1.（1）Explain whether particle X is in the center of a compression or a rarefaction.
（2）On Figure A, use $Y'$ to mark the equilibrium position of particle Y.
2.When the frequency of the sound is increased by 120Hz the next harmonic of the standing wave is formed in the pipe. Show that the length of the pipe is $142\,cm$.L≈ cm
