Sample Report

This sample report should help you understand what I expect of your reports.

Read it carefully and make a list of comments and/or questions that you may come across as you read it.

A student wrote this conclusion last semester.

You will find my comments in orange following each paragraph.

Name: Cynthia Astroloka

Partner(s): Emily Heinrich (fall 2001)

Date:  Any good day

Section: AST 1022L  - 0441

Experiment: Sample Report # 1

This is the Prelab (due at the beginning of class the day the experiment is performed)

Purpose

        The goal of this experiment is to study 1) the relationship between the impactor size and the diameter of the crater they form, and 2) the relationship between the height from which the impactor drops and the velocity of the impactor.

Theory

        The length of this section will vary depending on the experiment. You will mostly get the information from either the "introduction" or the "procedure."

        In the case of "Impact Craters" you could include answers to the following questions as I did for the slide presentation.

·       Describe the different theories that were used to interpret craters.

·       How are craters formed?

·       Why is there such a great interest in craters, i.e. what are the human and astronomical implications?

This is the rest of the report that is due 1 week after the experiment is performed.

Data Sheet, Graphs & Tables

        Below is a sample data sheet that I provided you for the "Impact Craters" experiment. For the graphs, simply follow this link Graphical Representation of Experimental Data.

IMPACT CRATERS - Spring 2002

Student Name: _________________________________________________________

Partner(s) Name(s): _____________________________________________________

Goal: Determine the relationship between the size of an impactor and the size of a crater.

Note:

1. When measuring diameters, measure it twice: 1) along the major axis, 2) minor axis.

2. Smooth the sand surface with an edge after each trial.

3. Position the meter stick on the edge of the tray.

1. Effect of Impactor Size

1. Error of Measurement

   Height (cm)	Impactor Diameter (cm)	Crater Diameter (cm)	Deviation (cm)	Deviation2 (cm2)
   100
   100
   100
   100
   100
   100
   Average Crater Diameter (cm)			SD2 (cm2)
   Standard Deviation s (cm)

2. Effect of Velocity Impactor Diameter = ____________________ (cm)

Questions

        Be sure to read the entire procedure & "Your Report" sections in your manuals. The questions are often times hidden within the text. A common mistake amongst students is not answering the question completely. Read the question carefully, and address all parts of it.

Sample Calculations:

          This is self-explanatory, just remember to include a sample of each calculation performed, and don't forget to accompany your results with UNITS!

Conclusion:

1)    Summary: For this experiment, you take a rudimentary solar telescope and position it so that it points toward the Sun. You then move the telescope until an image of the Sun projects itself through the lens and onto the white screen of the telescope. Once you have the image on the screen, you focus the image by moving the plates holding the lens and the screen up and down on the telescope until the image on the screen is at it's smallest and sharpest. You then measure the diameter of the image using a millimeter scale and measure the distance from the lens to the image using a meter stick. Take turns taking several measurements of the image and focal length and then take the average of the image lengths and average of the distance lengths to use in calculations. Next, you change the lens in the telescope and repeat the experiment with a different lens and thus a different image size and distance length. At no time should you ever look directly at the Sun because it could cause blindness. It is safe to view the Sun on the screen because it is a filtered image.

Her summary is not an example to follow since she writes a summary of the procedure followed during the experiment. Remember, I want you to write a paragraph or two about what you learned from the experiment, e.g. you learned that there is a linear/nonlinear relationship between the size of the impactor and the diameter of the crater they form, learned to take measurements using a high precision Vernier caliper, etc.

2)    Error Analysis: We found that the experiment worked very well. The diameter we calculated was very close to the true diameter, and we only had a 0.71% error for the first lens and a 2.66% error for the second lens.  Both of these error percentages beat Cassini's 10% error, which was thought to be a fairly good measurement, so our measurements were very good.  We found that although both lenses yielded low error percentages, the first lens with the smaller image gave us a better result than the second with the larger image.  The first lens had a power of 1.04 diopters and the second had a power of 0.53 diopters. 

In the above paragraph she presents a discussion of her results and compares them with the known accepted value (Cassini's measurements) to evaluate the reliability of her results.

From this information, I can infer that the larger the power of the lens in diopters, the smaller the image on the screen, and the more precise the measurements will be. While the first lens with the smaller image size and focal length seemed to be better for measuring distances, the second lens with the larger image and focal length was able to project a more detailed image of the Sun. Since the Sun was active on the day we observed it, we were able to detect a sunspot with the second lens. We also found that the smaller image size from the first lens coincided with a smaller focal length, and the larger image size from the second lens coincided with a larger focal length. This makes sense because if each of the ratios, i/f, from the two lenses equals the ratio s/d, the two ratios from the lenses, i/f, should equal one another. Thus as the image size increases, so should the focal length.

She proceeds to discuss what the percentages imply about the precision of the different lenses used.

On the day we did the experiment, the sky was pretty clear with only some intermittent clouds, so we were able to perform the experiment in a relatively short amount of time and without much difficulty. We had to wait a couple of times for the clouds to move away, but we didn't have to wait very long. However, if the sky were very cloudy when you were trying to perform the experiment, it might cause some error in calculations. If, for instance, you tried to measure the sun while a cloud was still partially covering the Sun or making it hazing on the screen, you could come up with a distorted measurement of the image. Also, if you tried to rush through the measurements to beat the clouds before they came back, you could end up with hasty, inaccurate measurements. To avoid errors such as these, it is best to wait to perform this experiment until you have a clear sky with only intermittent clouds. Once the sky is appropriate, you can perform the experiment, but there are still several other errors that can occur.

The above paragraph depicts the physical conditions present while performing the experiment. She goes even further to discuss the measures she would have taken had the conditions been unfavorable.

One problem we ran into was that the telescope couldn't lock into position, so the image was wobbling as we tried to measure it. This is probably where most of our error came from. It was very hard to tell the diameter to the exact millimeter, but we held the telescope as still as possible and tried our hardest to get an accurate measurement. If we were able to lock the telescope into position, I'm certain our results would be much more accurate. Error could have also come from inadequate focusing. We had to use our judgment to determine which image looked the best, and the method of focus didn't allow for much fine-tuning.  It was a very rough method of focusing, and it is hard to say if we focused the telescope to the right image. We did take steps to try to reduce this error, however. We focused and refocused the image three times and took three separate measurements and then averaged the image sizes and the focal lengths to come up with a more accurate image size and focal length to use in calculations. Another source of error is that the edge of the image was not as dark as the center of the image due to limb darkening, which is caused by the outer layer of the Sun's atmosphere being cooler and higher than the rest of the sun. Because it fades out a bit on the edges, it is hard to tell exactly where the edge of the Sun is on the image. Regardless of all of these possible sources for error, we came up with two fairly accurate measurements for the diameter of the Sun.

She finally describes many of the other problems that she encountered and how these problems affected the data.

It should now be obvious to you that this student was very methodical, but that is precisely what it is necessary in order to write such an excellent error analysis.

A couple of tips for writing a good conclusion:

1)    Take notes of the conditions while performing the experiment. (Weather, faulty equipment, precision of instruments?)

2)    Listen carefully to my comments. I will very often tell you the main sources of errors for a given experiment.

3)    Discuss your data fully, i.e. present your results and discuss their reliability - how do they compare with other experimental or theoretical values?

4)    Be very specific; never leave it up to the reader to imagine what you're trying to say!

5)    The conclusion need not be long. However, it needs to be self-consistent.