[填空题]
A loudspeaker producing sound of a single frequency is placed at a distance $1.5\,m$ in front of a barrier as shown in the diagram.
1.Describe the conditions for which standing waves occur.
2.(1)A microphone moves in a horizontal direction from the barrier to the speaker. The microphone detects loud sound at some positions while at others it detects low intensity sound. Explain why this happens.
(2)The microphone detects three positions of high intensity sound. On the axes given, sketch the relationship between the amplitude of oscillation of the air particles and the distance from the wall.
(3)The distance between two successive loud sound positions is 0.60 m. Calculate the frequency of the sound produced by the loudspeaker. The speed of sound in air is $340\,ms^{−1}$. $f$= Hz
3.The microphone is placed at the location where the sound is loudest. The barrier is then moved towards the loudspeaker until the sound at the microphone has become quiet. Calculate the distance the barrier has moved. Distance moved m
