General Physics 1 Lab - PHY 2048L Lab 6: Wave Mechanics Wave on a String / Optical Tweezers PhET Lab Date. Wave on a String

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1 General Physics 1 Lab - PHY 2048L Name Lab 6: Wave Mechanics Wave on a String / Optical Tweezers PhET Lab Date Author: Harsh Jain / PhET Source: Wave on a String Wave on a String Qualitative Description: 1. Under Simulations, click on Sound and Waves. Click on Wave on a String. Click on Run Now! Set up the controls as shown below. 2. Fixed vs. Loose End: Click on the green pulse button. Observe the pulse through one cycle. Click on yellow reset button and change the Fixed End to Loose End. Observe the pulse through one cycle. Repeat these steps if necessary and describe the difference in the reflected waves. 3. Fixed vs. No End: Reset the controls to the original settings. Click on the green pulse button. Observe the pulse through one cycle. Click on yellow reset button and change the Fixed End to No End. Observe the pulse through one cycle. Repeat these steps if necessary and describe the difference in the reflected waves. 4. High vs. Low Tension: Reset the controls to the original settings. Click on the green pulse button. Observe the pulse through one cycle. Click on yellow reset button and reduce the tension to two clicks above low. Observe the pulse through one cycle. Repeat these steps if necessary and describe the difference in the reflected waves. 5. Damping vs. No Damping: Reset the controls to the original settings. Click on the green pulse button. Observe the pulse through one cycle. Click on yellow reset button and move the damping slider to 30. Observe the pulse through one cycle. Repeat these steps if necessary and describe the difference in the reflected waves. As the amplitude of the wave decreases, the energy of the waves dissipates. Where does the energy go?

2 6. Two waves on a String: Reset the controls to the original settings, except click on the Loose End. Click on the green pulse button. When the pulse is about half way down the chain, click on the green pulse button a second time. Observe the two pulses through several cycles. When two "up" waves meet, what happens to center chain link when the pulses are completely overlapped? When "up" and "down" waves meet, what happens to center chain link when the pulses are completely overlapped? 7. Explore: Take some time to explore the Manual and Oscillate options and the effects of varying the amplitude, pulse width, damping and tension Quantitative Analysis: 1. Turn on the ruler and timer, set damping to zero and click the radio button for No End. 2. What happens to the speed of the wave as the tension slider is moved from high to low? 3. Use the ruler and timer to calculate the speed of the wave at high tension, low tension and in the middle. Speed Dis tan ce Time Distance 3. Time 4. Speed 5. High Tension Low Tension Medium (middle) Tension Click on Oscillate measure the wavelengths for each of the following while TENSION is set to LOW. To measure wavelength hit pause and use the ruler. 17. Frequency 18. Amplitude 19. Wavelength

3 5. How does changing the frequency affect the wavelength? How does changing the amplitude affect the wavelength? How does changing the frequency affect the energy of the wave? How does changing the amplitude affect the energy of the wave?

4 9. Now measure how the wavelength changes as the speed changes you will need to measure the speed and the wavelength. (hint for frequency 15 at high tension measure the length of half a wave and double it) 58. Frequenc y 59. Tension 60. Amplitude 61. Distanc e 62. Time 63. Speed 64. Wavelengt h Low Middle Low Middle High Middl e High How does changing the speed affect the wavelength if the frequency is constant? Why? Speed = Frequency x Wavelength. Can you prove this with your data? How?

5 Pre-Lab Questions: Objectives: 1. Investigate wave properties including amplitude, speed, and frequency and wavelength. 2. Investigate the effects of damping on a wave. Directions: Go to the PhET Website and find the simulation called Wave on a String (it s in the sound and waves area). Answer each of the following questions using a complete sentence. 1. Describe the difference in the waves produced when one end of the string is fixed, loose, and free. (Look carefully at the parts of the wave that appear to not move.) 2. If you change the amplitude of the wave produced, is there an effect on the wave s speed? If so, explain why you think this is so. 3. Define amplitude in your own words based upon your observations. 4. If you change the frequency of the wave produced, is there an effect on the wave s speed? If so, explain why you think this is so. 5. Define frequency in your own words based upon your observations. 6. If the frequency goes up, what happens to the length of the waves produced? What relationship do frequency and wavelength have? 7. If you change the tension of the string, is there an effect on the wave s speed? If so, explain why you think this is so. 8. If you increase the damping, what happens to the wave? If you decrease the damping, what happens to the wave? Why do you think this is so? 9. In terms of things we ve studied this year, what is damping similar to? 10. In this simulation, it is possible to completely eliminate the damping on the wave. Is this possible to do in real life? Why or why not? 5