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在“机械波”一章中讲到波的干涉时,课本上总是用水波的干涉来进行分析。但是用发波水槽来做水波干涉实验并用投影器投影到屏幕上时干涉条纹不十分清楚,效果不太好。而且有些学校还没有这些仪器。下面介绍一种用音叉来演示波的干涉实验。手拿不装共鸣箱的音叉的把。用小槌敲一下叉股,则音叉的两个叉股都发生机械振动,并都会发出轻微的声音,而且发出的声音是逐渐减弱的。这是因为叉股的振动是阻尼振动。但是两个叉股又是相干波源,即频率相同、振动方向相同、相差恒定。所以只要在小槌敲击一下叉股后,拿住音叉把的手的位置不动,而仅用手转动音叉把,则坐在四周的人都能听到时强时弱的声音。这是因为两个叉股发出的两列声波,在音叉转动中,它们从各
When the wave of interference is described in the chapter “Machine Waves,” textbooks always use the interference of waves to analyze. However, interference fringes are not very clear when the water wave interference experiment is performed with a wave-making water tank and the projector projects on the screen, and the effect is not very good. And some schools do not yet have these instruments. Here’s a tuning experiment that uses a tuning fork to demonstrate waves. Hand holding a tuning fork without a resonance box. With a small hammer knocking on the fork, the two forks of the tuning fork will vibrate mechanically and will make a slight sound, and the sound will gradually fade. This is because the vibration of the fork is a damped vibration. However, the two fork strands are coherent wave sources, that is, the same frequency, the same vibration direction, and a constant difference. Therefore, as long as the small gong knocks on the fork, the position of the hand holding the tuning fork does not move, and only the tuning fork is turned by hand, and people sitting around can hear strong and weak voices. This is because of the two rows of sound waves emitted by the two prongs, which rotate from one to the other in the tuning fork.