PH112L - Physics II Lab

Winter Term 2016

General Information

Instructor:    Galen C. Duree Jr., PhD

Office:    CL106 (The Department Office)                  Phone:    872-6025                        Box:    182


Office Hours:      9:30 AM - 10:30 AM   M T R  &  4:20 PM - 5:15 PM M T R F

The second experiments for our lab section were held on Friday, January 13, 2017, in BL114.  The experiments are entitled "Resonance in Strings" (a description of which can be found beginning on page 157 in the lab manual).

The lab reports are due in the green bin outside the PHOE department office by 5:30 PM on Friday, January 20, 2017.

For the "Resonance in Strings" experiment, you will be evaluating two models for waves on strings and evaluating a model for the wave speed for a particular tension.  The first part of the experiment will involve finding at least five (5) resonant frequencies for a particular tension in a string.  Make sure that you mention in your procedure section how you determined the correct resonant frequency for a particular mode of vibration.  Next, you will need to choose a single mode of vibration that was easy for you to work with in the first experiment (say, the n = 3 mode), and then change the weight hanging off the end and find the new frequency for the new tension.  Since you have done one tension already in the first experiment, you need to do four more (at a minimum) so that you have at least 5 different tensions.

In the Analysis Section, make a graph of frequency vs. mode number (n) WITH ERROR BARS!.  Fit a line to this and evaluate the model by seeing if a majority of the error bars for the points cross the fit line or not.  If they do, the model is appropriate for your situation.  If not, the model is not appropriate for your situation.  The slope of this line is equal to the fundamental frequency for the string.  Use this value (with its uncertainty) to determine the speed of waves on the string for the particular tension.  Compare this experimental value to the theoretical value of SQRT(Tension/mass per unit length) (again, make sure you include uncertainties!).  The second graph you should make is a plot of fn vs. SQRT(Tension), with error bars.  If a majority of the error bars for the points cross the fit line, the model is appropriate for your situation.  If not, the model is not appropriate for your situation.  The slope of this line contains the mass per unit length value.  Use this to determine the theoretical  wave speed and compare it to the experimental wave speed.  If the two values overlap within uncertainty, the wave speed model is appropriate for your situation.  If the two values do not overlap within uncertainty, the wave speed model is not appropriate for your situation.

Remember:  Departmental policy is that there should be one graph per page and it should be the only thing on that page.  Also, make sure that you label the axes and include appropriate units!

Download a copy of the Error Analysis Worksheet


Lab Report Format

A complete lab report must have the following sections:

Do not forget to update your Table of Contents and to number the pages in your lab notebook!

The first page of your report must have a title, the name of the P.I. (explicitly indicate who was the P.I.), the name of the lab assistant, and the date that the report was turned in (not the date that you performed the experiment!).

*Abstract - a BRIEF description of what you were investigating, how you conducted the experiment and your conclusions based on your experience.  The abstract should not be a discussion of what you are going to do in the lab.  The abstract cannot be written before you have analyzed your data.  In the lab notebook, skip a page or two so that you can write this in at the beginning of the report after you have analyzed your data.

Introduction - a discussion about any details that you think would help someone perform the experiment.  This should include a discussion about the model (equations that you are using) or the method selected for performing the tests.  If you use models (equations) in your analysis, list the models in this section and describe what each of the variables represent.

**Procedure - a detailed description of what you did in the lab.  At the beginning of this section, place the date and the time that you began the experiment.  This section must include a schematic, detailing how things were connected, where appropriate.  The raw data must appear in this section immediately following the description about how the data was taken.   A person must be able to read your procedure section and be able to duplicate your results without having the lab manual present.  Do not do any calculations in this section, just record how you performed the experiments and record the raw data.  If the data is taken by computer, you must specify the path and filename where the data is stored.   This information must be listed in this section right after the description of how the data was taken.  Do not simply list all of the files generated at the end of the section.

This section MUST be signed by the instructor before you leave the lab.  If you turn in a report without the signature, it will not be accepted!

Analysis - a sample of the calculations made in the lab.  This section should include a sample of the error calculations and propagation of errors used in your analysis.   The final data that you are analyzing to generate conclusions, the values with appropriate uncertainties, must be shown in this section.  The actual calculations for each one does not have to be included, as long as you show an example for one, but you may include them all if you wish.  The calculations may be done by the computer, but include printouts of the worksheet in your lab book.  Any graphs or printouts that are placed in your notebook must occupy one whole page and be trimmed to fit within the page and not hang outside of the notebook.

*Conclusion - this section must have a conclusion that is based on your experiments and analysis.  If your conclusions do not following logically from your analysis, your grade will be deducted significantly.  This section must also contain a brief description of significant factors that you think affected your data, in particular, the uncertainties in your data (factors that contributed to the error in your experiment).  A good thing to keep in mind is to think of this report as a report you are submitting as part of your job responsibilities.   If you do not think your boss would accept what you have to say, it is a safe bet that I will not like it either.

The asterisks indicate the sections that I will pay closest attention to.

Modified January 13, 2017 by Galen C. Duree Jr.