Physics 211-213 Laboratory Instructions
Lab Rules
1)You will combine into teams of two to four people and equitably share the workload.
2)You will not use your calculator.
3)You are allowed to discreetly enter and exit the room.
4)You will not return malfunctioning equipment to the carts.
5)You will attend the entire lab unless you submit a completed report to eLearn before the end of the lab session.
6)You will clean up after yourself and push your chair in when you complete the lab.
Lab Reports
Your grade for this section of the course will be determined by your lab reports. Reports must be typed and submitted to eLearn. The format of the reports must be as follows:
1)Title
2)Feedback
3)Purpose
4)Pre-Lab
5)Raw Data, Initial Uncertainty Estimation, and Observations
6)Calculations, Uncertainty Propagation, and Graphs
7)Conclusion and Acknowledgements
Lab Teams
Data, calculations, photos, and graphs may be the same as your teammates’. Your purpose, uncertainty justifications, observations, and conclusion must be unique. Basically, numbers are allowed to be the same, but words are not. Copying and pasting sentences constitutes a violation of academic honesty (see the syllabus).
Pre-Lab
Some labs will include a “pre-lab”. This is usually a computer simulation with accompanying questions. Answer the questions using the provided form, and then have someone from your lab group check your work with your instructor before proceeding with the lab.
Writing Conventions
There are a number of conventions for reporting numbers. There are also some rules I want to impose on your words.
1)Never begin a number with a decimal. Put a zero in front of it if necessary.
2)The least significant digit of a number and its uncertainty must be the same.
3)Do not truncate zeroes when they are significant. Excel will often do this automatically, so you must undo the damage.
4)Use complete sentences. Be careful when starting a sentence with “to”, especially in your purpose statement.
5)Do not capitalize words such as “law” unless they are in a title or begin a sentence.
6)Do capitalize last names when they are in the name of an equation. Do not capitalize last names when they are used as a unit.
7)Do not use the following expressions: close (doubtful relevance), actual, human uncertainty (vague), in conclusion (redundant), good. Use the following expressions: overlapped, experimental, theoretical, and verified.
8)Do not refer to a variable as its unit (ex: amperage).
9)Do use first person (I, me, we, us, our …), especially when it promotes the use of active voice. Avoid excessive use of passive voice.
Feedback
Copy and paste the instructor’s feedback from your previous lab report (or previous version of the report if it is a resubmission). This will obviously be skipped in your first lab report of the term. Please note that feedback will tend to be negative as it will focus on areas for improvement. Even an excellent lab report can receive negative feedback.
Purpose
The purpose of each lab is usually to test a physical principle (Newton’s second law, Archimedes’ principle, etc.) or a physical constant. Use this verb or something similar in your purpose statement (not “explore”, “study”, or “verify”).
Raw Data, Initial Uncertainty Estimation, and Observations
Do not summarize the procedure unless you invented or altered it. Include relevant observations. This includes numerical data as well as descriptions of things that cannot be quantified.
Most numerical data should include an initial estimate of the uncertainty (sometimes called “error”)including a specific verbal justification of this estimate. The uncertainty in raw data can be attributed to equipment (manufacturer, condition, scale limit), user (vision, attentiveness, reaction time, etc.), and object being measured (inherent difficulty in measuring the object itself). Do not simply report the uncertainty of a measurement as the scale limit of the measuring device. Here are some special cases:
- Table values can be assumed to have an uncertainty of ± 1 for the last reported digit unless otherwise specified.
- The accepted value of g in Salem is 9.806 ± 0.001 m/s2.
- For hand held timing devices, the uncertainty is typically about 0.10 seconds, even when using a timing device with a smaller scale limit. This may be adjusted up or down depending upon the particular situation.
- Uncertainty in digital thermometers is typically ± 1.0 °C even when the scale limit is smaller.
This section must be clearly identified as distinct from the Calculations, Uncertainty Propagation, and Graphs section. You should not do any math (or present any results based on math) in the raw data section with the exceptions of unit conversions and converting percentage uncertainties to absolute uncertainties.
Calculations
Use a spreadsheet such as Excel for your calculations. A portion of the spreadsheet may be cut and pasted into your report. Do not submit your spreadsheet.
You do not need to provide every detail of your calculations or uncertainty propagation, but please include a sample calculation and uncertainty propagation for each different equation you use. The sample calculations and uncertainty propagation should use both symbols and numbers.
Avoid rounding during intermediate steps of a calculation. Round at the end of your calculations. Base your rounding on a reasonable estimate of the significant digits, but do not agonize over this point.
UncertaintyPropagation
This portion of the lab is totally tedious and totally necessary.
- x: result of calculation
- a, b, and c: numbers used for calculation
- sx: uncertainty in result
- sa, sb, and sc: uncertainty in numbers used for calculation
1)Addition and Subtraction
x = a + b – c
2)Multiplication and Division
x = a * b/c
3)Exponentiation(including square root whereb = ½)
x = ab
4)Trigonometry Function
x = trig(a)
These techniques of uncertainty propagation should be repeated for each operation in the order required by the rules of mathematics until you reach your final calculated values. Compare the range of experimental values obtained to the theoretical value or range of theoretical values in order to reach a conclusion. If overlap exists, then your experiment confirms the theory. If overlap does not exist, then your experiment denies the theory.
Uncertainty Shortcuts
1)If you are taking the average of n values with the same error, sa, then the uncertainty in the average value will be sa/sqrt(n).
2)If sb = 0, sc = 0, and x = a + b – c , then sx = sa.
3)If sb = 0, sc = 0, and x = a * b/c, then sx = sa * b/c. The uncertaintyin a value will typically be zero for mathematically defined constants like π or 2, but not for empirical constants like g.
Graphs
Notes: Do not make a graph if the lab instructions do not specifically demand one. You may share graphs among your lab group after the first week.
We will use Excel for its high speed and accuracy of graphing, and to enhance error analysis. Consult your instructor if you need help using Excel. If you use Excel 2007 for your graphs, then use the following instructions:
1)If all data has the same error, then put the x values in one column and the y values in the next column. If the data has individualized error, then create a table as shown below.
2)Highlight the x and y values alone. You should hold down the control button to add a column that is not contiguous.
x / ± / y / ±1.0 / 0.5 / 6.0 / 1.0
2.0 / 0.5 / 7.0 / 2.0
3.0 / 0.3 / 8.0 / 1.0
4.0 / 1.0 / 9.0 / 0.5
5.0 / 0.2 / 8.0 / 0.8
3)Click on the “Insert” tab.
4)Click on “Scatter” with the option that does not connect dots. You should now have a graph.
5)Click on the first chart layout which should add a title and axis labels.
6)Click on the axis labels and rewrite them. Include units.
7)Click on the title and rewrite or remove it. Do not repeat the axis labels.
8)If there is only one set of data, then remove the legend. If there is more than one set of data, then do the following:
- Right click somewhere on empty space in the graph
- Choose “Select Source Data”.
- Click on “Series 1” and the “Edit” button.
- Write the name of the data series and hit “OK”.
- Repeat steps c and d until all data is named.
9)On the “Layout” tab, click on “Gridlines”, “Primary Horizontal Gridlines”, and “None”.
10)Remain on the “Layout” tab. Click on “Error Bars” and “Error Bars with Percentage”.
11)Click on “Error Bars” and “Error Bars with Percentage”.
12)Right-click on one of the horizontal error bars in your graph and select “Format Error Bars”. Enter either a fixed value or “Custom” and “Specify Value”.
13)Repeat the above step with the vertical error bars.
14)Add a trend line if you have a logical reason for doing so.
- Under the “Layout” tab, choose “Trendline” and then the type of line justified by theory, usually linear.
- Right click on the trend line and choose “Format Trendline”.
- Click on the boxes for “Display Equation” and “Display R-squared”. Click “Close”.
- Click on the text box you just created and change the x and y to meaningful symbols.
15)You may choose to reduce the amount of empty space.
- Right click on an axis you wish to shrink.
- Change the minimum (and perhaps maximum) to “fixed” and enter values. Click “Close”.
Conclusion and Acknowledgements
Your conclusion must correctly and definitively state whether or not the experiment supports the scientific principle based on the results of your uncertainty propagation. If theoretical and experimental values do not overlap, then do not explain it away by saying that you underestimated the uncertainty. Here are some suggested phrases you can use:
- “The theoretical and experimental values overlapped, therefore this experiment supports …”
- “The theoretical and experimental values did not overlap, therefore this experiment does not support …”
Your conclusion must also include specific and feasible improvements or extensions to the lab you would make given additional time and material. The improvements could address clarifying the lab instructions, feasible ways to reduce uncertainty, or feasible ways to increase the range of the data. Feasible means things that could be done with reasonable time, money, and safety. You are welcome to provide additional, unfeasible suggestions for improvement.
Your conclusion must also include acknowledgement of any assistance you received in gathering raw data or performing calculations. You may also acknowledge the scientists who developed the physics tested in the lab, the person who wrote the lab instructions (Erik Jensen), or the person who assembled the lab equipment (Matt Azevedo, Liz Traver, and team). Do not include acknowledgements of inanimate objects, pets, or supernatural beings.
Grading
If you submit a report with major errors or omissions, you will earn a zero and may be asked to resubmit your report. You will earn up to two points for each of the following items:
1)Pre-Lab: The pre-lab, if any, must be complete and correct.
2)Format and Writing: The lab report must be organized as specified and reasonably neat. I enforce a high standard of clarity. This includes, but is not limited to, correct grammar and spelling.
3)Raw Data, Initial Uncertainty Estimation, and Observations: Careful lab work will result in high accuracy and precision for numerical data. Astute observations and thorough writing are also important. Numerical data should include an initial estimate of the uncertainty including a specific verbal justification of this estimate.
4)Calculations, Uncertainty Propagation, Graphs: Calculations and uncertainty propagation must be performed correctly. Graphs must be in the above specified format.
5)Conclusion and Acknowledgements: Your conclusion must include the following: a comparison of experimental and theoretical values, a confirmation or denial of the scientific principle, suggestions for improvement, and acknowledgements.
Here are some common violations:
Violation / SectionThe sections are mixed. The most commonly mixed sections are the raw data and calculations sections. / Format and Writing
The file size exceeds 2 MB. / Format and Writing
Instructor’s feedback from the previous lab is missing. / Format and Writing
More than one file is uploaded (separately uploading pre-labs, pictures, spreadsheets, or graphs for example) / Format and Writing
The list of banned words is ignored. / Format and Writing
There are spelling or grammar errors. / Format and Writing
Number writing conventions (see conventions 1 through 3 on page 1) are violated. / Format and Writing
The initial uncertainty estimation is not verbally justified for all raw data. / Raw Data
The initial uncertainty estimation considers only equipment uncertainty or uses the scale limit of the device as the default uncertainty. / Raw Data
Observations in the raw data are weak or nonexistent. / Raw Data
Raw data do not demonstrate thorough and careful lab technique / Raw Data
The graphs, when requested, are missing, incorrect, or not in the specified format (connecting the dots, including grid lines, including a meaningless title or legend, missing axis labels or units) / Calculations
There is a meaningless, gratuitous graph. / Calculations
The calculations are missing or incorrect. / Calculations
Sample calculations are missing or only provide symbols. / Calculations
The calculations are missing uncertainty propagation. / Calculations
The conclusion does not specifically address the purpose or the purpose is too narrow. Usually the purpose is to test a theory or law, so the conclusion should state specifically that the experiment either supports or does not support the theory or law in question. / Conclusion
The conclusion is contrary to the evidence. This is usually the case when experimental and theoretical values do not overlap, yet this discrepancy is explained away. Do not do this. / Conclusion
The conclusion is based on a calculated percentage difference between experimental and theoretical values and a comparison to an arbitrary standard. Ex: “We were within 10%, so we think…” Do not do this unless specifically instructed to do so for a particular lab. / Conclusion
The conclusion does not include acknowledgements. / Conclusion
The conclusion does not include specific and feasible suggestions for improvement. / Conclusion
Due Date and “Check Out” Policy
Completed reports are due on eLearn at the end of the 3-hour lab session. You may receive an extension (due by 11:55 pm the following day) if you undergo a “check out” during the last 15 minutes of the lab session. The “check out” will consist of your lab group presenting your findings to the instructor. Failure to follow these rules may result in a zero on your lab report.
Keep a copy of this document for reference throughout the term.