Representing Waves

Waves on water are very familiar, especially here in Jersey, but to analyse waves properly we need an instrument that offers suitable measurement features. The instrument that we use is called a Cathode Ray Oscilloscope (CRO).

You have seen sound waves on a CRO screen in the lab and you can revisit this learning online using resources that have been made public specifically to support remote teaching during the lock-down. The resources that we will be using are from Cambridge Assessment and can be accessed here… https://learning.cambridgeinternational.org/classroom/course/view.php?id=3453

Start by watching the main video (it is less than four minutes long). You should write bullet-point notes to summarise the main facts as you watch the video, pausing it as necessary so that you don’t miss new information as you write about the previous fact!

You may wish to use the Cornell Notes system that was covered previously (click here to revisit that post).

Next, click on the link for the Virtual Experiment. This uses the same video but with pause points that are signalled by an alert in the top left corner of the video and blue dots on the playback track at the bottom of the screen. The alerts refer to questions that you must answer as you work your way through the video. You should click on the alerts when they appear to get more details and to pause the playback. To access the worksheet needed for the virtual experiment, click here.

At one point in the video, you are asked to discuss the different waveforms in small groups: since we cannot gather together, you should simply pause the video and describe the differences in the waveforms to yourself (either on paper, or just in your head).

You do not need to email the worksheet as the answers were all in the video and extra help is available on pages 56-57 in your CGP Edexcel Physics Complete Revision and Practice book.

But there is other work that you do need to send to Mr Tarrant for feedback;

1. The last alert asks you to make two measurements from the CRO screen in the video. You must submit these two values (numbers of squares, measured as accurately as you can).

2. The last alert also includes two discussion questions: you must submit your own (brief) answers to these questions.

3. At the end of the video, you are asked how to use two microphones and a CRO to measure the speed of sound. This technique is explained in the top half of p58 in your revision guide. You must write this method in your own words and email it to Mr Tarrant for feedback. A good way to explain the technique is by making three drawings that shown the CRO trace when;

• the two microphones are alongside each other at the same distance from the loudspeaker
• the second microphone is a random distance further away than the other microphone
• the second microphone is one wavelength further away than the other microphone

Then explain how to use these drawing to identify the measurements needed (one using a ruler and the other by looking at the setting on the signal generator) to calculate the speed of sound.