Resonance in a Closed Pipe Criteria graded: DC, DPP, CE Problem Question: What is the effect of a change in the frequency of a sound wave on the velocity of that sound wave at a constant room temperature? (don’t forget to include a hypothesis!!) Manipulated Variable—frequency of a tuning fork Responding Variable—length of resonating air column corresponding to the largest amplitude of the fundamental standing wave. (in order to calculate the velocity of the sound wave in the air column) Controlled Variable—temperature of the room/water in tube Note on Variables: You will be manipulating the frequency of the tuning fork (the source of the wave) and measuring the lengt h of the resonating air column that gives you the loudest tone that matches the pitc h of the tuning fork (when held to your ear). Using the measured length and the known frequency, you will be able to calculate the average velocity of sound. Materials Needed: - Safety Glasses—Mandatory - Aluminum tuning forks of 5 different frequencies (1024 Hz, 512 Hz, 256 Hz, 384 Hz, and 320 Hz) - Rubber tuning fork mallet - Resonance tube (mm increments) - 1000 mL cylinder - ~800 mL – 1000 mL water Procedure: 1. Fill your graduated cylinder to between 700 and 800 mL with wat er. 2. Place the resonance tube upside -down into the graduated cylinder 3. Strike one of the tuning forks (as demonstrated in class) with the rubber hammer. (NOT on the table or on your shoe!) 4. Place the vibrating end of the tuning fork over the resonance tube, being very careful not to hit the glass tube with the vibrating metal. Make sure that the tuning fork is oscillating above, but parallel to, the resonance tube as shown in class, and that the vibrating end of the fork is approximately 1 cm above the resonance tube. 5. Move the column and the tuning fork up and down until you hear the loudest tone. Record this length of the air column. Make sure the tuning fork remains the same distance above the opening of the resonanc e tube. 6. Repeat steps 3 – 5 with the same tuning fork for an appropriate number o f trials. 7. Repeat steps 3 – 6 for all remaining tuning fork frequencies. Data collection: Create a data table to show the data collected in this lab. Data Processing: Show clear steps that you took to logically reach your conclusion. Additional analysi s: 1. The accepted speed of sound at 20.0° C is 343 m/s. By what percent did your calculated value differ from this value? (if you got significantly different values for your different frequencies, calculate a different % difference for each…if they’re re ally similar, calculate an average speed of sound first…then calculate a % difference.) 2. What do you think are some possible reasons for this variation (NOT experimental errors as reasons…)? 3. How would your values for resonant lengths change if we had us ed an open pipe rat her than the closed pipe? Why? Conclusion and Evaluation: Complete a conclusion bas ed on the IB lab grading rubric.
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