THE LAB REPORT WRITEUP

This introductory section is intended for you, the student, to use as a guide and reference for general physics laboratory. It is important that you read the practices and procedures as outlined in this introduction.

The labs are intended to provide you with

1. hands-on experience with the concepts we have been going over in class;
2. practice in taking measurements (a very important part of being in science or engineering);
3. and practice working in groups.

Laboratory Report Format

Each group must submit a lab report for each experiment performed. The following format is recommended and should be adhered to closely unless your instructor decides otherwise. Use 8 1/2" x 11" paper and do not write on the back of the sheets. Write legibly or (even better) type, and use proper grammar. Points will be taken off for misspelled words and incorrect grammar. A small portion of your grade may be based on your in-lab performance.

1. Cover Sheet:
Title of experiment, your name, date that experiment was performed, partner's names.  (First and last names. Get the spelling right!)

2. Abstract:
1-3 sentences. Write a concise statement of the principle result that is described in this report.   This should include what you were trying to measure (or do) and then whether your measurement (or tinkering) managed to agree with the expectations.

3. Theory:
1-2 paragraphs.  Summarize the basic physics of your experiment. Include equations and other principle things the reader would need to know in order to understand the experiment.  Keep it short!

4. Experimental procedure:
Describe briefly how you carried out the experiment. Do not include relatively trivial things like turning on a switch. On the other hand, you should include descriptions of how you determine things that are necessary to the anticipated results.  This should be very short as well.  Mention the particular pitfalls in data taking that you discovered and managed to maneuver around.  You may need to recreate a wiring diagram or draw the apparatus in order to refer to it later during discussion.

5. Raw data and numerical analysis
Present the raw data you took here, and any calculations performed on it (if needed) in obtaining the result. It is important to note that “raw data” are the exact measurements that you took. Don’t subtract something off in your head before writing any numbers down – write whatever is on the measuring device and then perform analysis. This is important in order to find mistakes (yes, they happen!) later on. Data and analysis should be easy to follow, in tabular form.  Poor data recording skills lead to poor writeups.  If your raw data and subsequent analysis are illegible, the grade will suffer.

6. Graphs:
Include title, labeled axes, smooth lines through experimental data points, and slope calculations. Each graph should convey a complete message and be fully understandable without referring to any other section in the report. When calculating a slope of a line on a graph, make sure to choose grid points that are at the front and end of the line respectively in order to have a large difference in x and y values. Draw a triangle or otherwise connect the two points. Label Dx and Dy, and calculate the slope right there on the graph. Scales should be chosen so that the plot should takes up the whole page, so that plotting accuracy is increased. An example

If you use a spreadsheet program (e.g. Excel) to plot your data and fit a line, be sure to set scales so that the data takes up the whole page (as above) and that the equation for the fitting line is displayed on the graph as well as the line itself.

7. Results:
This is a very important section of the lab!  It is here that it becomes clear whether your data agree with the accepted value(s) or are self-consistent. Calculate final experimental results, standard or accepted values, if they exist, and percent errors and/or percent differences.

Percent error is used when comparing a result to an accepted value.
% error = ( (X - X_s) / X_s ) x 100
where X_s = a standard or accepted value
X = an experimental value

Percent difference is used when comparing two results from different experimental methods. The average of the two measurements is probably closer to the actual value than either measurement. So, the average is used in the denominator.
% difference = ( (X₁- X₂) / X_avg )x 100 %
where X₁ = an experimental value,
X₂ = an experimental value obtained by another method,
X_avg = (X₁ + X₂ )/2
        = the average value of X₁ and X₂

This section should be a concise, tabulated summary of your results.

Two examples are as follows:

1. Comparing to an accepted value: Percent error

--	Accepted value	Experimental Result	Percent Error
Acceleration Due to gravity	980 cm/sec^2	960 cm/sec^2	-2%

2. Comparing two measurements of the same quantity: Percent difference

--	Method #1	Method #2	Percent Difference
Initial Velocity of Projectile	21 ft/sec	19.7 ft/sec	+ 6.4%

As a rule of thumb, ±3% error is considered reasonable for experimental results. However, don't always expect to get accuracy this good. In some experiments an 80% error might be reasonable because of component tolerances. The nature of the experiment has a bearing on the expected accuracy.

8. Discussion/Conclusion:
This section should not be a rehash of your results. Discuss how your results demonstrate basic principles of physics. Most importantly, conclude whether your data agree with the accepted value(s) or are self-consistent. Give possible reasons for errors, personal observations, suggestions, and any other comments you feel are pertinent. (Hint: In discussing errors, think carefully about the limits of the measuring apparatus.)

Last updated 30 August, 2002
Scott Nutter