[填空题]
A thin tube with a length of L is immersed in water and fixed to the base of a container of liquid by a string. The length of the tube above the surface of the water is X and inside the water is Y.
A speaker is emitting a single-frequency sound above the tube. For particular values of X, a standing wave is established in the tube.
1.Explain how a standing wave is formed in this tube.
2.The frequency of the sound is 200 Hz. It is found that the smallest value of X for which a standing wave is established in the tube is 42.0 cm. Estimate the speed of sound in the tube. v= $ms^{-1}$
3.The string is cut and the tube rises in the container, decreasing the length of tube Y inside the water. When Y is 22cm, the second harmonic of the standing wave is formed. Calculate the total length of the tube.L= m
