Physics 3U Speed of Sound Lab
Objective: The purpose of this experiment is to calculate the speed of sound in air and compare the calculated values with the accepted value and the average value obtained by the class.
Apparatus:
Air column (plastic or glass)
tuning forks: 256 Hz, 512 Hz, 1024 Hz (shared with other groups)
Container for water
wireless device (one per lab group)
rubber stopper (for striking tuning forks)
Method:
1. While performing this experiment, record any additional observations that seem relevant.
2. At the start of the lab the teacher will measure air temperature and announce it to everyone so that it can be recorded.
3. For a speed of sound of approximately 340 m/s, calculate the shortest length of air column needed to resonate with a tuning fork.
4. Fill the air column with water so that the length of the air in the column matches the value calculated in #3.
5. Strike the tuning fork against the rubber stopper and move the vibrating fork over the air column to see if there is resonance.
6. Adjust the water level to get maximum resonance. It is suggested that you pour water from and back into your water container for efficiency and ease. Measure the length of the air for maximum resonance. Use the wireless device to enter this value into the spreadsheet on Google Docs.
7. If the tuning fork is 1024 Hz, repeat steps 3 – 6 for the second and, if possible, third resonant lengths.
8. Repeat steps 3 – 7 for the other tuning forks.
Observations:
Any measurements and other observations should be noted in this section of the lab write-up.
Calculations/Analysis:
1. Determine the wavelength of the standing wave in each case, based on the length of the air column.
2. Calculate the speed of sound in each case, based on the frequency and wavelength.
3. Determine your best estimate of the speed of sound based on your information.
4. Compare your speed of sound with both the accepted value and the average value determined by the class. Calculate percentage error in both cases.
Sources of Error:
When you make measurements, make a note of the possible measurement error. For example, in this lab it will be difficult to determine an accurate length for maximum resonance. Make your best estimate of the uncertainty involved (e.g. maximum resonance occurred for an air column of approximate 14 – 17 cm). In the previous example, the best estimate of length would be 15.5 cm with an uncertainty of plus/minus 1.5 cm.
After making your calculations based on your best estimate of your measurements, you need to determine the possible range of uncertainty from experimental errors. Do the calculations again using the possible measurement values that will create the largest answer. Repeat this calculation using the possible measurement values that will create the smallest answer. The range from smallest answer to largest answer is the range of uncertainty for your calculation.
For this lab, at minimum you should quantify the possible effect of errors in measuring air column length
Conclusions:
State your calculated value the speed of sound as well as the numerical value of the uncertainty in that calculation because of measurement and other errors. Give the percentage error in comparison with accepted value and class average.
Improvements:
Suggest any improvements to this lab which would make the lab easier, more efficient, or more accurate. Remember, be thorough and be specific. A general statement of “use better tools to measure” is not useful, practical, thorough, or specific and will earn you no credit for application.
In particular, suggest ways that would reduce the effects of the most serious measurement error discussed above.
Rubric for Evaluation
Category/Criterion / Level 4 (do it with high effectiveness) / Level 3
(do it right) / Level 2 (do more than the obvious) / Level 1 (do the obvious)
Thinking/Investigation
- analyzing and interpreting results / Analyses and interprets results with a high degree of effectiveness / Analyses and interprets results with considerable of effectiveness / Analyses and interprets results with some effectiveness / Analyses and interprets results with limited effectiveness
Communication – expression and organization of ideas and information / expresses and
organizes ideas
and information
with a high
degree of
effectiveness / expresses and
organizes ideas
and information
with considerable
effectiveness / expresses and
organizes ideas
and information
with some
effectiveness / expresses and
organizes ideas
and information
with limited
effectiveness
Application – applies dynamics knowledge to lab / Applies heat/energy knowledge with a high degree of effectiveness / Applies heat/energy knowledge with considerable effectiveness / Applies heat/energy knowledge with some effectiveness / Applies heat/energy knowledge with limited effectiveness
***to save paper, please hand in this rubric with the lab***