3.14.2 Experimental instruments
Fixed string vibration experiment platform,string line,weight,wedge,etc.
Figure 3.14.1 The fixed string vibration platform
1—Mechanical vibration source with adjustable frequency digital display;2—Vibrating reed;
3—String line;4—Movable bracket;5—Movable edge bracket;6—Ruler;7—Fixed pulley;
8—Weight and weight plate;9—Transformer;10—Experiment platform;11—Experiment table
The experimental device is shown in Figure 3.14.1.One end of the metal string is tied to the reed of the adjustable frequency digital mechanical vibration source that can vibrate in the horizontal direction.The frequency range is continuously adjustable from 0 to 200 Hz,with the smallest change in frequency of 0.01 Hz.The other end of the string is suspended with a weight plate 8 through a fixed pulley 7;there is a movable bracket 4 near the vibrating device(vibrating reed),and there is another movable edge bracket on the experimental device that can move left or right along the direction of the string,and the movable blade can support the string 5.The pulley 7 is fixed on the experimental platform 10,and the friction generated by it is very small and can be ignored.If the mass of the weight(including the weight plate)suspended at the lower end of the string is m,the tension along the string is T=mg.When the wave source vibrates,a transverse wave propagating to the right is formed on the string line;when the wave propagates to the point where the movable edge bracket and the string line intersect,the string line is blocked by the two walls of the edge at this point and cannot vibrate,and the wave is reflected to form a reflected wave propagating to the left.The superposition of two waves with opposite propagation directions forms a standing wave.(https://www.daowen.com)
During the experiment,the input plug of the transformer(black shell)is connected to the 220 V AC power supply,and the output end(five-core aviation cable)is connected to the aviation seat on the host.Turn on the power switch 1 on the panel of the digital display vibration source(the panel of the vibration source is shown in Figure 3.14.2)The digital tube 5 on the panel displays the vibration frequency of the vibration source***.**Hz.Press the▲(increase frequency)or▼(decrease frequency)key in the frequency adjustment 2 to change the vibration frequency of the vibration source,and adjust the amplitude adjustment knob 4 on the panel to make the vibration source conduct a vibration output;when the vibration source is not required to vibrate,you can press the reset button 3 on the panel to reset,and the digital tube display is cleared.
Figure 3.14.2 The Vibration control panel
1—Power switch;2—Frequency adjustment;3—Reset button;
4—Amplitude adjustment;5—Frequency indication
