没有幻灯片标题-哈尔滨工程大学物实验教学中心.pptVIP

声速的测量与示波器的使用 理学院 * Determining the Velocity of Sound and Using the Oscilloscope 1.Purpose: Understand the relationship between the sound speed and the air state parameters Understand the function of the piezoelectricity transducer. Understand deeply the theory of standing waves and vibrating interfering Mastering the using of the oscilloscope. Mastering a method of measuring sound speed. 2.Principle: (1) sound speed in theory is expressed as (1) In the formula (1), T0=273.15 K，t is condition temperature, formula (1) can be used to calculate the sound speed in air. (2) the theory of sound speed measuring By the relationship between speed v frequency f and wavelength λ: v=fλ (2) so when we measure out f and λ , we can calculate v by formula (2). The instruments are showed in Fig.1. Fig.1 Instruments used to measure λ The transducer S1 is used to emit sound wave . The transducer S2 is used to receive sound wave. When the standing wave appears, the sound wave received by S2 is strongest, and the phenomena can be displaced by the oscilloscope. A standing wave pattern is an interference phenomenon. It is formed as the result of the perfectly timed interference of two waves passing through the same medium. A standing wave pattern is not actually a wave; rather it is the pattern resulting from the presence of two waves of the same frequency with different directions of travel within the same medium. One characteristic of every standing wave pattern is that there are points along the medium which appear to be standing still. These points, sometimes described as points of no displacement, are referred to as nodes. There are other points along the medium which undergo vibrations between a large positive and large negative disp