Exp. 14 – Standing Waves
Dear Students,
Please carefully read the instructions given in your lab manual (pages 131-136) about this experiment and follow the outlined procedure (pages 136-140). We have prepared a short video demonstrating the working principles of the experiment which is linked below. But due to the nature of this experiment, it is difficult to collect data from a video. Instead you will use applets that simulate closely what happens in a real experiment. You will perform your lab using these applets and collect data directly from simulations.
Virtual lab video:
https://www.youtube.com/watch?v=CozFMPV3MTA
Required Software:
The applets require installing Wolfram Player, which is available for free from this link: https://www.wolfram.com/player/
Applets (Please read the instructions below):
Investigation 1: Standing Waves – Investigation 1.cdf
Investigation 2: Standing Waves – Investigation 2.cdf
Investigation 1:
When you open the CDF file, please wait for the applet to fully load. Depending on your computer’s speed, it could take up to 10 secs to fully load this applet. Below is a screenshot of what you should see.
There is a resonator running at 120 Hz on the left. A pail is attached to this resonator with a string through a pulley. The total weight of this pail and the weights you put in it allows you to control the tension on the string. The total mass of the pail + weights is displayed on the pail. The resonator is always on, but most of the time nothing special happens on the string. But, for certain mass values you get a standing wave pattern. The one shown on the picture below is for n=9, has 10 nodes and requires a total mass of 52 grams. Your task in this investigation is to determine those special mass values required to form standing wave patterns on the string and measure distances between consecutive nodes for n=2,3,..,7.
In the real experiment, each node to node distance comes out slightly different because of the difficulties involved in taking the measurements. To mimic this, we added a little wobble to the string, so you should expect your measurements to be slightly different in this simulation as well.
The physical length of the string is 1.5 m (from the resonator to the pulley). You can use this to determine the actual physical distances when you measure lengths on your computer screen. For example, if the string on your computer screen is 23.3 cm long, you will need to scale up all your measurements by a factor of 150 cm / 23.3 cm = 6.44.
Please follow the instructions given in your lab manual and collect your data from this applet.
Investigation 2:
When you open the CDF file, please wait for the applet to fully load. Depending on your computer’s speed, it could take up to 30 secs to fully load this applet. When the applet is fully loaded, the button on the top should read “Stopped”. Below is a screenshot of what you should see. If the applet does not fit in your screen, you can use the zoom function.
You can control the level of the water in the sound apparatus by moving the water reservoir on the right with your mouse. When you click on the button at the top, you engage the tuning fork and it will emit a sound at the frequency displayed just below the button. You should be able to hear the sound the tuning fork makes from your computer’s speakers. Similar to the first investigation, your task in this investigation is to form standing wave patterns. This time the standing waves will form in air and we won’t be able to see them, but you will hear the sound of the tuning fork being amplified and it will become more intense when the resonance condition is obtained. The tuning fork only rings for 10 seconds, and the top button will switch to “Stopped”. You will need to click on the button again to engage it for another 10 secs.
Please follow the instructions given in your lab manual and collect your data from this applet.
