Workout: Wave speed

Read

Wave speed

Launch

he PhET simulation, Wave on a string

Set up

Set the switches to "No end" and "Pulse". Click on "Rulers" (in the lower right) and "Timer", and set the damping to 0. Move the timer so it is next to the start button. Your screen should look like that shown below. (It might be useful to set the sim to "Slow Motion" to better do your measurements.)

Answer these questions

1. Press the green button on the device that generates the pulse. Use the timer to measure the time that is takes to move a certain distance along the ruler. (Say from when the front edge passes 4 to when it reaches 6.) Does the velocity you get from this measurement agree with what you inferred in the last assignment from comparing the time to generate the pulse and its width?
2. The slider that allows you to adjust the tension does not have any scale markings. Move the slider to the marker between "Low" and "High". If this were half the tension when the slider was at "High", what would you expect the velocity of the pulse to be?
3. Choose some way to measure the speed of the pulse when the tension is at the halfway mark. What did you get?
4. Does this agree with your calculation?
5. Explain why the pulse is narrower when the tension is less.

Joe Redish, Spring 2017