Part IV. Standing Waves with Fixed End Settings: Fixed End, High Tension, Oscillate, No Damping, Amplitude: 0.1 cm Observe what happens to the wave as it travels down the line. If the frequency is just right, the reected wave interferes with the original wave and creates a standing wave composed of nodes and antinodes. A node will always exist at the xed end because the phase of the wave is inverted upon reection and therefore always destructively interferes at that position. (Since the amplitude is so small, the oscillating end is nearly xed as well.) Adjust the frequency until maximum amplitude results. You will want one large crest/trough in the middle, looking almost like a jump rope. (You can use the reference line to help you detect small changes in the amplitude as you ne tune the frequency.) Since this will have one antinode and two nodes, the length of string is one-half of a wavelength. Record the frequency and wavelength in the table below. Use the wave speed equation to determine the speed. Adjust the frequency to obtain two, three and four antinodes. Measure and record your values for these waves in the table. Wavelength Wave Speed ___ ___ ___ ___ How did the wave speed compare in your four trials. How does this compare to the value you calculated in Part III. Explain. Part V. Standing Waves with Loose End Settings: Loose End, High Tension, Oscillate, No Damping, Amplitude: 0.1 cm Observe what happens to the wave as it travels down the line. If the frequency is just right, the reected wave interferes with the original wave and creates a standing wave composed of If the frequency is just right, the reected wave interferes with the original wave and creates a standing wave composed of nodes and antinodes. Instead of a node, an antinode will always exist at the loose end. (This happens because the phase of the wave is not inverted upon reection from a loose end and therefore always constructively interferes at that position.) Adjust the frequency until maximum amplitude results. You will want one large crest/trough at the loose end. (You can use the reference line to help you detect small changes in the amplitude as you ne tune the frequency.) Since this will have one antinode and one node, the length of string is one-fourth of a wavelength. Record the frequency and wavelength in the table below. Use the wave speed equation to determine the speed. Adjust the frequency to obtain two, three and four antinodes. (One of those antinodes will always be at the loose end.) Measure and record your values for these waves in the table. Wavelength Wave Speed ___ ___ ___ ___ How did the wave speed compare in your four trials? How does this compare to the value you calculated in Part III. Do you notice a pattern with your frequencies? Explain. Part VI. Practice Questions (Questions 1 and 2) A rope is vibrating so as to form the standing wave pattern shown at the right. 1. How many nodes are present in the rope? a. 3 b. 4 c. 5 d. 8 e. 10 2. What harmonic is shown in the pattern? a. third b. fourth c. fth d. eighth "I .l '1 4' 'I .l" 1 l'f' l'1v'\\.'l'_'l' Part VI. Practice Questions (Questions 1 and 2) A rope is vibrating so as to form the standing wave pattern shown at the right. 1. How many nodes are present in the rope? a. 3 b. 4 c. 5 d. 8 e. 10 2. What harmonic is shown in the pattern? a. third b. fourth c. fifth d. eighth 3. A guitar string has a fundamental frequency of 120 Hz. What is the frequency of the third harmonic of the string? a. 40 HZ b. 80 Hz c. 160 Hz d. 180 Hz e. 360 Hz 4. A demonstration of interference is done in class. A SlinkyTM is stretched out from end to end. Three cups are placed on the ground, positioned just to the side of the SlinkyTM. Two pulses are introduced into each end at the same time. The pulses travel towards each other as shown in the diagram. What will be observed after the pulses pass by each other? a. All three cups will be knocked over. b. Cups 1 and 3 will be knocked over; cup 2 will be left standing. c. Only cup 2 will be knocked over; cups 1 and 3 will be left standing. d. Nothing will happen to any of the cups; they will all be left standing.Wave Interference Investigation Use the Wave on a String activity from PhET to investigate wave interference. Part I. Loose End Interference Settings: Loose End, Low Tension, Pulse, N0 Damping Send a pulse down the medium and observe what happens to the wave as it travels down the line. Is the wave reected off the end or inverted and then reected? (Does it hit and bounce or ip and bounce?) Part 11. Fixed End Interference Settings: Fixed End, Low Tension, Pulse, No Damping Send a pulse down the medium and observe what happens to the wave as it travels down the line. Is the wave reected off the end or inverted and then reected? (Does it hit and bounce or ip and bounce?) Part III. Measure Wave Speed Settings: Fixed End, High Tension, Pulse, No Damping Open the Ruler and Timer. Make note of the length of the string. Send a pulse down the medium. When the pulse gets back to the beginning of the string, start the timer. Determine the time for 10 trips along the length of string (5 full round trips) in order to get a good average for the time to go once. Use this information along with the length of the string to determine the speed of the wave. Part IV. Standing Waves with Fixed End Settings: Fixed End, High Tension, Oscillate, No Damping, Amplitude: 0.1 cm Observe what happens to the wave as it travels down the line